Preparation of 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof in transgenic organisms

Abstract

The present invention relates to a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof by culturing organisms, in particular yeasts. Furthermore, the invention relates to the preparation of the nucleic acid constructs required for preparing the genetically modified organisms and to said genetically modified organisms, in particular yeasts, themselves.

Claims

1. A method for preparing 7-dehydrocholesterol and/or cholesterol, the method comprising the steps of: culturing a yeast organism which, compared to the wild type, has an increased activity of at least one of the activities selected from the group consisting of: 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2, 5-desaturase activity of a 5-desaturase having the amino acid sequence having at least 90% sequence identity to SEQ ID NO: 8; and 24-reductase activity of a 24-reductase having the amino acid sequence having at least 90% sequence identity to SEQ ID NO: 14; and wherein the yeast organism additionally have increased HMG-CoA-reductase activity of HMG-CoA-reductase having the amino acid sequence having at least 90% sequence identity to SEQ ID NO: 24; harvesting the yeast after culturing; and isolating the 7-dehydrocholesterol and/or cholesterol after harvesting.

2. The method of claim 1, wherein the yeast organism additionally has, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of lanosterol C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity.

3. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 2.

4. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence of SEQ ID NO: 2.

5. The method of claim 1, wherein the yeast organism has an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 8.

6. The method of claim 1, wherein the yeast organism has an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence of SEQ ID NO: 8.

7. The method of claim 1, wherein the yeast organism has an increased 24-reductase activity of a 24-reductase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 14.

8. The method of claim 1, wherein the yeast organism has an increased 24-reductase activity of a 24-reductase having the amino acid sequence of SEQ ID NO: 14.

9. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 2, and an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 8.

10. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence of SEQ ID NO: 2, and an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence of SEQ ID NO: 8.

11. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 2, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 14.

12. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence of SEQ ID NO: 2, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence of SEQ ID NO: 14.

13. The method of claim 1, wherein the yeast organism has an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 8, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 14.

14. The method of claim 1, wherein the yeast organism has an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence of SEQ ID NO: 8, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence of SEQ ID NO: 14.

15. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 2, an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 8, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence having at least 95% sequence identity to SEQ ID NO: 14.

16. The method of claim 1, wherein the yeast organism has an increased 8-7-isomerase activity of a 8-7-isomerase having the amino acid sequence of SEQ ID NO: 2, an increased 5-desaturase activity of a 5-desaturase having the amino acid sequence of SEQ ID NO: 8, and an increased 24-reductase activity of a 24-reductase having the amino acid sequence of SEQ ID NO: 14.

17. The method of claim 1, wherein the yeast organism additionally has, compared to the wild type, increased HMG-CoA-reductase activity of an HMG-CoA-reductase having the amino acid sequence of SEQ ID NO: 24.

18. The method of claim 1, wherein the increased activity is from increased gene expression of a nucleic acid introduced into the yeast organism encoding the 8-7-isomerase, 5-desaturase, or 24-reductase.

19. The method of claim 3, wherein the increased 8-7-isomerase activity is from increased gene expression of a nucleic acid introduced into the yeast organism encoding the 8-7-isomerase.

20. The method of claim 5, wherein the increased 5-desaturase activity is from increased gene expression of a nucleic acid introduced into the yeast organism encoding the 5-desaturase.

21. The method of claim 7, wherein the increased 24-reductase activity is from increased gene expression of a nucleic acid introduced into the yeast organism encoding the 24-reductase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates the vector denoted pUG6-tHMG.

(2) FIG. 2 illustrates the vector denoted pUG6-ERG1.

(3) FIG. 3 illustrates the vector denoted pUG6-ERG11.

(4) FIG. 4 illustrates the vectors denoted pFlat3 and pFlat1.

(5) FIG. 5a illustrates the vectors denoted pFlat1-EBP and pFlat3-EBP.

(6) FIG. 5b illustrates the vector denoted pFlat3-SC5D.

(7) FIG. 5c illustrates the vector denoted pFlat1-Ebp.

(8) FIG. 5d illustrates the vector denoted pFlat4-D24R.

(9) FIG. 6 illustrates the vector denoted pFlat4.

(10) FIG. 7 illustrates the vector denoted pFlat4-ERG4.

(11) It is an object of the present invention to provide a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, which method has advantageous properties such as a higher product yield.

(12) We have found that this object is achieved by a method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, in which organisms are cultured which have, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity.

(13) An increased activity compared to the wild type means, in the case of the starting organism not having said activity, that said activity is caused. In the case of the starting organism already having said activity, an increased activity compared to the wild type means an activity increased by a percentage.

(14) 8-7-Isomerase activity means the enzyme activity of a 8-7-isomerase, also referred to as 8-7-sterol isomerase.

(15) A 8-7-isomerase means a protein which has the enzyme activity of converting zymosterol to cholesta-7,24-dienol.

(16) Accordingly, 8-7-isomerase activity means the amount of zymosterol converted or the amount of cholesta-7,24-dienol formed by the protein 8-7-isomerase in a particular time.

(17) In the case of an increased 8-7-isomerase activity compared to the wild type, thus the amount of zymosterol converted or the amount of cholesta-7,24-dienol formed by the protein 8-7-isomerase in a particular time is increased in comparison with the wild type.

(18) This increase in 8-7-isomerase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the 8-7-isomerase activity of the wild type.

(19) 5-Desaturase activity means the enzyme activity of a 5-desaturase, also referred to as lathosterol 5-desaturase or sterol C5-desaturase.

(20) A 5-desaturase means a protein which has the enzyme activity of converting cholesta-7,24-dienol to cholesta-5,7,24-trienol.

(21) Accordingly, 5-desaturase activity means the amount of cholesta-7,24-dienol converted or the amount of cholesta-5,7,24-trienol formed by the protein 5-desaturase in a particular time.

(22) In the case of an increased 5-desaturase activity compared to the wild type, thus the amount of cholesta-7,24-dienol converted or the amount of cholesta-5,7,24-trienol formed by the protein 5-desaturase in a particular time is increased in comparison with the wild type.

(23) This increase in 5-desaturase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the 5-desaturase activity of the wild type.

(24) 24-Reductase activity means the enzyme activity of a 24-reductase, also referred to as 24-dehydrocholesterol reductase.

(25) A 24-reductase means a protein which has the enzyme activity of converting the double bond between C24 and C25 of cholesterol compounds to a single bond, for example converting cholesta-5,7,24-trienol to 7-dehydrocholesterol or zymosterol to lathosterol or cholesta-7,24-dienol to cholesta-7-enol.

(26) Accordingly, 24-reductase activity means preferably the amount of cholesta-5,7,24-trienol converted or the amount of 7-dehydrocholesterol formed by the protein 24-reductase in a particular time.

(27) In the case of an increased 24-reductase activity compared to the wild type, thus the amount of cholesta-5,7,24-trienol converted or the amount of 7-dehydrocholesterol formed by the protein 24-reductase in a particular time is increased in comparison with the wild type.

(28) This increase in 24-reductase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the 24-reductase activity of the wild type.

(29) A wild type means the corresponding not genetically modified starting organism. Preferably and, in particular in those cases in which the organism or the wild type cannot be classified unambiguously, wild type means a reference organism for increasing the 8-7-isomerase activity, increasing the 5-desaturase activity, increasing the 24-reductase activity, reducing the C24-methyltransferase activity described below, reducing the 22-desaturase activity described below, increasing the HMG-CoA-reductase activity described below, increasing the lanosterol C14-demethylase activity described below, increasing the squalene-epoxidase activity described below, increasing the squalene-synthetase activity described below and increasing the sterol-acyltransferase activity described below and also for increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof. This reference organism is preferably the yeast strain Saccharomyces cerevisiae AH22.

(30) In the method of the invention, organisms are cultured which, compared to the wild type, have an increased activity of at least one of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity.

(31) In a preferred embodiment, organisms are cultured which, compared to the wild type, have an increased 8-7-isomerase activity, 5-desaturase activity or 24-reductase activity.

(32) In a particularly preferred embodiment of the method of the invention, the organisms have, compared to the wild type, an increased activity of at least two of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity.

(33) Particularly preferred combinations are 8-7-isomerase activity and 5-desaturase activity, increased in comparison to the wild type, 8-7-isomerase activity and 24-reductase activity, increased in comparison to the wild type, and 5-desaturase activity and 24-reductase activity, increased in comparison with the wild type.

(34) In a very particularly preferred embodiment of the method of the invention, the organisms have, compared to the wild type, an increased 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity.

(35) The 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity and also the HMG-CoA-reductase activity, lanosterol C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity, which are described below, may be increased independently of one another in various ways, for example by eliminating inhibiting regulatory mechanisms at the expression and protein level or by increasing, compared to the wild type, gene expression of the corresponding nucleic acids, i.e. nucleic acids encoding a 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase.

(36) Likewise, gene expression of the corresponding nucleic acid may be increased compared to the wild type in various ways, for example by inducing the appropriate genes by activators, i.e. by inducing the 8-7-isomerase gene, the 5-desaturase gene, the 24-reductase gene, the HMG-CoA-reductase gene, the lanosterol C14-demethylase gene, the squalene-epoxidase gene, the squalene-synthetase gene or the sterol-acyltransferase gene by activators, or by introducing one or more gene copies of the appropriate nucleic acids, i.e. by introducing one or more nucleic acids encoding a 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase into the organism.

(37) Increasing the gene expression of a nucleic acid encoding a 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase means according to the invention also manipulation of the expression of endogenous 8-7-isomerases, 5-desaturases, 24-reductases, HMG-CoA reductases, lanosterol C14-demethylases, squalene epoxidases, squalene synthetases or sterol acyltransferases, which are intrinsic to the organism, in particular to the yeasts.

(38) This may be achieved, for example, by modifying the promoter DNA sequence of genes coding for 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase. Such a modification which causes an increased rate of expression of the relevant gene may be carried out, for example, by deleting or inserting DNA sequences.

(39) As described above, it is possible to modify expression of the endogenous 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase by applying exogenous stimuli. This may be carried out using particular physiological conditions, i.e. by applying foreign substances.

(40) Furthermore, a modified or increased expression of endogenous 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA reductase, lanosterol C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase genes may be achieved by interaction of a regulatory protein which is not present in the untransformed organism with the promoter of said genes.

(41) A regulator of this type may be a chimeric protein which consists of a DNA-binding domain and a transcriptional activator domain, as described, for example, in WO 96/06166.

(42) In a preferred embodiment, the 8-7-isomerase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a 8-7-isomerase.

(43) In a further preferred embodiment, gene expression of a nucleic acid encoding a 8-7-isomerase is increased by introducing into the organism one or more nucleic acids encoding a 8-7-isomerase.

(44) For this purpose, it is possible to use in principle any 8-7-isomerase gene, i.e. any nucleic acid encoding a 8-7-isomerase.

(45) In the case of genomic 8-7-isomerase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate 8-7-isomerase.

(46) Examples of 8-7-isomerase genes are nucleic acids encoding a murine 8-7-isomerase (nucleic acid: Seq. ID. No. 1, protein: Seq. ID. No. 2) or a human 8-7-isomerase (nucleic acid: Seq. ID. No. 3, protein: Seq. ID. No. 4) (Braverman, N. et al., (1999): Mutations in the gene encoding

(47) 3-hydroxysteroid-8,7-isomerase cause X-linked dominant Conradi-Hunermann syndrome, Nat. Genet. 22(3), 291-294), or else nucleic acids encoding proteins which have the activity of a 8-7-isomerase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a C8-isomerase Saccharomyces cerevisiae (ERG2) (Nucleic acid: Seq. ID. No. 5, protein: Seq. ID. No. 6) (Ashman, W. H. et al. (1991): Cloning and disruption of the yeast C-8 sterol isomerase gene. Lipids. August; 26(8):628-32).

(48) In this preferred embodiment, thus at least one further 8-7-isomerase gene is present in the transgenic organisms of the invention, compared to the wild type.

(49) The number of 8-7-isomerase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(50) All of the nucleic acids mentioned in the description may be, for example, an RNA sequence, DNA sequence or cDNA sequence.

(51) Preferred 8-7-isomerase genes are nucleic acids encoding proteins which have a high substrate specificity for zymosterol. Therefore, preference is given in particular to 8-7-isomerase genes and to the corresponding 8-,7-isomerases of mammals and to the functional equivalents thereof.

(52) Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ.

(53) ID. NO. 2 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 2, and having the enzyme property of a 8-7-isomerase.

(54) The sequence SEQ. ID. NO. 2 represents the amino acid sequence of Mus musculus 8-7-isomerase.

(55) Further examples of 8-7-isomerases and 8-7-isomerase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 2.

(56) The Homo sapiens 8-7-isomerase (Seq. ID. No. 4), for example, is 74% identical to the Mus musculus 8-7-isomerase (Seq. ID. No. 2).

(57) Further examples of 8-7-isomerases and 8-7-isomerase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 1, by hybridization techniques and PCR techniques in a manner known per se.

(58) The term substitution means in the description the replacement of one or more amino acids by one or more amino acids. Preference is given to carrying out conservative replacements in which the replacing amino acid has a similar property to that of the original amino acid, for example replacement of Glu by Asp, Gln by Asn, Val by Ile, Leu by Ile, Ser by Thr.

(59) A deletion is the replacement of an amino acid by a direct bond. Preferred positions for deletions are the polypeptide termini and the linkages between the individual protein domains.

(60) Insertions are introductions of amino acids into the polypeptide chain, with a direct bond formally being replaced by one or more amino acids.

(61) Identity between two proteins means identity of the amino acids over the in each case entire length of the protein, in particular the identity which is calculated by comparison with the aid of the Lasergene software from DNASTAR Inc., Madison, Wis. (USA), using the Clustal method (Higgins D G, Sharp P M. Fast and sensitive multiple sequence alignments on a microcomputer. Comput Appl. Biosci. 1989 Apr. 5(2):151-1) and setting the following parameters: TABLE-US-00001 Multiple alignment parameter: Gap penalty 10 Gap length penalty 10 Pairwise alignment parameter: K-tuple 1 Gap penalty 3 Window 5 Diagonals saved 5

(62) Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 2 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 2, in particular according to the above program algorithm with the above set of parameters.

(63) In a further, particularly preferred embodiment, the 8-7-isomerase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus 8-7-isomerase (SEQ. ID. NO. 2).

(64) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(65) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(66) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

(67) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 1 is introduced into the organism.

(68) The sequence SEQ. ID. NO. 1 represents the Mus musculus cDNA which encodes the 8-7-isomerase of the sequence SEQ ID NO. 2.

(69) Furthermore, all of the 8-7-isomerase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(70) In a preferred embodiment, the 5-desaturase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a 5-desaturase.

(71) In a further preferred embodiment, gene expression of a nucleic acid encoding a 5-desaturase is increased by introducing into the organism one or more nucleic acids encoding a 5-desaturase.

(72) For this purpose, it is possible to use in principle any 5-desaturase gene, i.e. any nucleic acid encoding a 5-desaturase.

(73) In the case of genomic 5-desaturase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate 5-desaturase.

(74) Examples of 5-desaturase genes are nucleic acids encoding a murine 5-desaturase (nucleic acid: Seq. ID. No. 7, protein: Seq. ID. No. 8) or a human 5-desaturase (nucleic acid: Seq. ID. No. 9, protein: Seq. ID. No. 10) (Nishi, S. et al., (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. Acta, 1490, (1-2), 106-108), or else nucleic acids encoding proteins which have the activity of a 5-desaturase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a Saccharomyces cerevisiae C5-desaturase (ERG3) (nucleic acid: Seq. ID. No. 11, protein: Seq. ID. No. 12), (Arthington, B. A. et al. (1991): Cloning, disruption and sequence of the gene encoding yeast C-5 sterol desaturase. Gene. June 15; 102(1):39-44.).

(75) In this preferred embodiment, thus at least one further 5-desaturase gene is present in the transgenic organisms of the invention, compared to the wild type.

(76) The number of 5-desaturase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(77) Preferred 5-desaturase genes are nucleic acids encoding proteins which have a high substrate specificity for cholesta-7,24-dienol. Therefore, preference is given in particular to 5-desaturase genes and to the corresponding 5-desaturases of mammals and to the functional equivalents thereof.

(78) Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 8 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 8, and having the enzyme property of a 5-desaturase.

(79) The sequence SEQ. ID. NO. 8 represents the amino acid sequence of Mus musculus 5-desaturase.

(80) Further examples of 5-desaturase and 5-desaturase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 2.

(81) The Homo sapiens 5-desaturase (Seq. ID. No. 10), for example, is 84% identical to Mus musculus 5-desaturase (Seq. ID. No. 8).

(82) Further examples of 5-desaturases and 5-desaturase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 7, by hybridization techniques and PCR techniques in a manner known per se.

(83) Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 8 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 8, in particular according to the above program algorithm with the above set of parameters.

(84) In a further, particularly preferred embodiment, the 5-desaturase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus 5-desaturase (SEQ. ID. NO. 8).

(85) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(86) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(87) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

(88) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 7 is introduced into the organism.

(89) The sequence SEQ. ID. NO. 7 represents the Mus musculus cDNA which encodes the 5-desaturase of the sequence SEQ ID NO. 8.

(90) Furthermore, all of the 5-desaturase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(91) In a preferred embodiment, the 24-reductase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a 24-reductase.

(92) In a further preferred embodiment, gene expression of a nucleic acid encoding a 24-reductase is increased by introducing into the organism one or more nucleic acids encoding a 24-reductase.

(93) For this purpose, it is possible to use in principle any 24-reductase gene, i.e. any nucleic acid encoding a 24-reductase.

(94) In the case of genomic 24-reductase nucleic acid sequences from eukaryotic sources, which contain introns, preferably already processed nucleic acid sequences such as the corresponding cDNAs are to be used, if the host organism is unable to or cannot be enabled to express the appropriate 24-reductase.

(95) Examples of 24-reductase genes are nucleic acids encoding a murine 24-reductase (nucleic acid: Seq. ID. No. 13, protein: Seq. ID. No. 14) or a human 24-reductase (nucleic acid: Seq. ID. No. 15, protein: Seq. ID. No. 16) (Waterham, H. R. et al.: Mutations in the 3-Hydroxysterol 24-Reductase Gene Cause Desmosterolosis, an Autosomal Recessive Disorder of Cholesterol Biosynthesis, Am. J. Hum. Genet. 69 (4), 685-694 (2001)), or else nucleic acids encoding proteins which have the activity of a 24-reductase, for example due to a broad substrate specificity, such as, for example, nucleic acids encoding a Saccharomyces cerevisiae 24-reductase (ERG4) (nucleic acid: Seq. ID. No. 17, protein: Seq. ID. No. 18) (Lai, M. H. et al., (1994): The identification of a gene family in the Saccharomyces cerevisiae ergosterol biosynthesis pathway. Gene. March 11; 140(1):41-9).

(96) In this preferred embodiment, thus at least one further 24-reductase gene is present in the transgenic organisms of the invention, compared to the wild type.

(97) The number of 24-reductase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(98) Preferred 24-reductase genes are nucleic acids encoding proteins which have a high substrate specificity for cholesta-5,7,24-trienol. Therefore, preference is given in particular to 24-reductase genes and to the corresponding 24-reductase of mammals and to the functional equivalents thereof.

(99) Accordingly, preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 14 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 14, and having the enzyme property of a 24-reductase.

(100) The sequence SEQ. ID. NO. 14 represents the amino acid sequence of Mus musculus 24-reductase.

(101) Further examples of 24-reductases and 24-reductase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 14.

(102) The Homo sapiens 24-reductase (Seq. ID. No. 16), for example, is 96% identical to Mus musculus 24-reductase (Seq. ID. No. 14).

(103) Further examples of 24-reductases and 24-reductase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 13, by hybridization techniques and PCR techniques in a manner known per se.

(104) Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 14 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 14, in particular according to the above program algorithm with the above set of parameters.

(105) In a further, particularly preferred embodiment, the 24-reductase activity is increased by introducing into organisms nucleic acids which encode proteins comprising the amino acid sequence of Mus musculus 24-reductase (SEQ. ID. NO. 14).

(106) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(107) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(108) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

(109) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 13 is introduced into the organism.

(110) The sequence SEQ. ID. NO. 13 represents the Mus musculus genomic DNA which encodes the 24-reductase of the sequence SEQ ID NO. 14.

(111) Furthermore, all of the 24-reductase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(112) In a further preferred embodiment of the method of the invention, organisms are cultured which have, compared to the wild type, a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and 22-desaturase activity in addition to the above-described genetic modifications.

(113) In a further particularly preferred embodiment, organisms are cultured which have, compared to the wild type, a reduced C24-methyltransferase activity and a reduced 22-desaturase activity in addition to the above-described genetic modifications.

(114) A reduced activity means both the reduced and the complete elimination of said activity. Reducing an activity therefore also comprises a reduction in the amount of the corresponding protein in the organism up to a complete absence of the corresponding protein, which can be tested, for example, via missing detectability of the corresponding enzyme activity or missing immunological detectability of the corresponding proteins.

(115) A C24-methyltransferase activity means the enzyme activity of a C24-methyltransferase.

(116) A C24-methyltransferase means a protein which has the enzyme activity of converting zymosterol to fecosterol (ergosta-8,24(28)dienol).

(117) Accordingly, C24-methyltransferase activity means the amount of zymosterol converted or the amount of fecosterol formed by the protein C24-methyltransferase in a particular time.

(118) In the case of a reduced C24-methyltransferase activity compared to the wild type, thus the amount of zymosterol converted or the amount of fecosterol formed by the protein C24-methyltransferase in a particular time is reduced in comparison with the wild type.

(119) The C24-methyltransferase activity is reduced preferably to at least 90%, further preferably to at least 70%, further preferably to at least 50%, further preferably to at least 30%, more preferably to at least 10%, still more preferably to at least 5%, in particular to 0%, of the C24-methyltransferase activity of the wild type. Therefore, particular preference is given to eliminating the C24-methyltransferase activity in the organism.

(120) 22-desaturase activity means the enzyme activity of a 22-desaturase.

(121) A 22-desaturase means a protein which has the enzyme activity of converting ergosta-5,7-dienol to ergosta-5,7,22,24-tetraen-3.-ol.

(122) Accordingly, 22-desaturase activity means the amount of ergosta-5,7-dienol converted or the amount of ergosta-5,7,22,24-tetraen-3.-ol formed by the protein 22-desaturase in a particular time.

(123) In the case of a reduced 22-desaturase activity compared to the wild type, thus the amount of ergosta-5,7-dienol converted or the amount of ergosta-5,7,22,24-tetraen-3.-ol formed by the protein 22-desaturase in a particular time is reduced in comparison with the wild type.

(124) The 22-desaturase activity is reduced preferably to at least 90%, further preferably to at least 70%, further preferably to at least 50%, further preferably to at least 30%, more preferably to at least 10%, still more preferably to at least 5%, in particular to 0%, of the 22-desaturase activity of the wild type. Therefore, particular preference is given to eliminating the 22-desaturase activity in the organism.

(125) The reduction in C24-methyltransferase activity and/or 22-desaturase activity may be carried out independently of one another by different cell-biological mechanisms, for example by inhibiting the corresponding activity at the protein level, for example by adding inhibitors of the corresponding enzymes or by reducing gene expression of the corresponding nucleic acids encoding a C24-methyltransferase or 22-desaturase, compared to the wild type.

(126) In a particularly preferred embodiment of the method of the invention, the C24-methyltransferase activity and/or the 22-desaturase activity are reduced compared to the wild type by reducing the gene expression of the corresponding nucleic acids encoding a C24-methyltransferase or 22-desaturase.

(127) Likewise, gene expression of the nucleic acids encoding a C24-methyltransferase or 22-desaturase may be reduced compared to the wild type in various ways, for example by

(128) a) introducing nucleic acid sequences which can be transcribed to an antisense nucleic acid sequence which is capable of inhibiting the C24-methyltransferase activity and/or 22-desaturase activity, for example by inhibiting the expression of endogenous C24-methyltransferase and/or 22-desaturase activity,

(129) b) overexpression of homologous C24-methyltransferase nucleic acid sequences and/or 22-desaturase nucleic acid sequences, which leads to cosuppression,

(130) c) introducing nonsense mutations into the endogene by means of introducing RNA/DNA oligonucleotides into the organism,

(131) d) introducing specific DNA-binding factors, for example factors of the zinc finger transcription factor type, which cause a reduction in gene expression or

(132) e) generating knockout mutants, for example with the aid of T-DNA mutagenesis or homologous recombination.

(133) In a preferred embodiment of the method of the invention, gene expression of the nucleic acids encoding a C24-methyltransferase or 22-desaturase is reduced by generating knockout mutants, particularly preferably by homologous recombination.

(134) Therefore, preference is given to using an organism which has no functional C24-methyltransferase gene and/or 22-desaturase gene.

(135) In a preferred embodiment, knockout mutants are generated, i.e. the C24-methyltransferase-gene target locus and/or the 22-desaturase-gene target locus are deleted with simultaneous integration of an expression cassette containing at least one of the nucleic acids described above or below, which encode a protein whose activity is increased in comparison with the wild type, by homologous recombination.

(136) For this purpose, it is possible to use nucleic acid constructs which, in addition to the expression cassettes described below which contain promoter, coding sequence and, where appropriate, terminator and in addition to a selection marker at the 3 and 5 ends, described below, contain nucleic acid sequences which are identical to nucleic acid sequences at the start and the end of the gene to be deleted.

(137) After selection by recombinase systems, the selection marker may preferably be removed again, for example via IoxP signals at the 3 and 5 ends of the selection marker, using a Cre recombinase (Cre-IoxP system).

(138) In the preferred organism Saccharomyces cerevisiae, the C24-methyltransferase gene is the gene ERG6 (SEQ. ID. NO. 19). SEQ. ID. NO. 20 represents the corresponding Saccharomyces cerevisiae C24-methyltransferase (Hardwick, K. G. et al.: SED6 is identical to ERG6, and encodes a putative methyltransferase required for ergosterol synthesis. Yeast. February; 10(2):265-9).

(139) In the preferred organism Saccharomyces cerevisiae, the 22-desaturase gene is the gene ERG5 (SEQ. ID. NO. 21). SEQ. ID. NO. 22 represents the corresponding Saccharomyces cerevisiae 22-desaturase (Skaggs, B. A. et al: Cloning and characterization of the Saccharomyces cerevisiae C-22 sterol desaturase gene, encoding a second cytochrome P-450 involved in ergosterol biosynthesis, Gene. 1996 Feb. 22; 169(1):105-9).

(140) In a further preferred embodiment of the method of the invention, organisms are cultured which have, in addition to the above-described modifications, an increased activity of at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity, compared to the wild type.

(141) HMG-CoA-reductase activity means the enzyme activity of an HMG-CoA reductase (3-hydroxy-3-methylglutaryl-coenzyme-A reductase).

(142) HMG-CoA reductase means a protein which has the enzyme activity of converting 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate.

(143) Accordingly, HMG-CoA-reductase activity means the amount of 3-hydroxy-3-methylglutaryl-coenzyme A converted or the amount of mevalonate formed by the protein HMG-CoA reductase in a particular time.

(144) In the case of an increased HMG-CoA-reductase activity compared to the wild type, thus the amount of 3-hydroxy-3-methylglutaryl-coenzyme A converted or the amount of mevalonate formed by the protein HMG-CoA reductase in a particular time is increased in comparison with the wild type.

(145) This increase in HMG-CoA-reductase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the HMG-CoA-reductase activity of the wild type.

(146) Lanosterol C14-demethylase activity means the enzyme activity of a lanosterol C14-demethylase.

(147) Lanosterol C14-demethylase means a protein which has the enzyme activity of converting lanosterol to 4,4-dimethylcholesta-8,14,24-trienol.

(148) Accordingly, lanosterol C14-demethylase activity means the amount of lanosterol converted or the amount of 4,4-dimethylcholesta-8,14,24-trienol formed by the protein lanosterol C14-demethylase in a particular time.

(149) In the case of an increased lanosterol C14-demethylase activity compared to the wild type, thus the amount of lanosterol converted or the amount of 4,4-dimethylcholesta-8,14,24-trienol formed by the protein lanosterol C14-demethylase in a particular time is increased in comparison with the wild type.

(150) This increase in lanosterol C14-demethylase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the lanosterol C14-demethylase activity of the wild type.

(151) Squalene-epoxidase activity means the enzyme activity of a squalene epoxidase.

(152) Squalene epoxidase means a protein which has the enzyme activity of converting squalene to squalene epoxide.

(153) Accordingly, squalene-epoxidase activity means the amount of squalene converted or the amount of squalene epoxide formed by the protein squalene epoxidase in a particular time.

(154) In the case of an increased squalene-epoxidase activity compared to the wild type, thus the amount of squalene converted or the amount of squalene epoxide formed by the protein squalene epoxidase in a particular time is increased in comparison with the wild type.

(155) This increase in squalene-epoxidase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the squalene-epoxidase activity of the wild type.

(156) Squalene-synthetase activity means the enzyme activity of a squalene synthetase.

(157) Squalene synthetase means a protein which has the enzyme activity of converting farnesyl-pyrophosphate to squalene.

(158) Accordingly, squalene-synthetase activity means the amount of farnesyl-pyrophosphate converted or the amount of squalene formed by the protein squalene synthetase in a particular time.

(159) In the case of an increased squalene-synthetase activity compared to the wild type, thus the amount of farnesyl-pyrophosphate converted or the amount of squalene formed by the protein squalene synthetase in a particular time is increased in comparison with the wild type.

(160) This increase in squalene-synthetase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the squalene-synthetase activity of the wild type.

(161) Sterol-acyltransferase activity means the enzyme activity of a sterol acyltransferase.

(162) Sterol acyltransferase means a protein which has the enzyme activity of converting 7-dehydrocholesterol to corresponding acetylated 7-dehydrocholesterol.

(163) Accordingly, sterol-acyltransferase activity means the amount of 7-dehydrocholesterol converted or the amount of acetylated 7-dehydrocholesterol formed by the protein sterol acyltransferase in a particular time.

(164) In the case of an increased sterol-acyltransferase activity compared to the wild type, thus the amount of 7-dehydrocholesterol converted or the amount of acetylated 7-dehydrocholesterol formed by the protein sterol acyltransferase in a particular time is increased in comparison with the wild type.

(165) This increase in sterol-acyltransferase activity is preferably at least 5%, further preferably at least 20%, further preferably at least 50%, further preferably at least 100%, more preferably at least 300%, still more preferably at least 500%, in particular at least 600%, of the sterol-acyltransferase activity of the wild type.

(166) In a preferred embodiment, the HMG-CoA-reductase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding an HMG-CoA reductase.

(167) In a particularly preferred embodiment of the method of the invention, gene expression of a nucleic acid encoding an HMG-CoA reductase is increased by introducing into the organism a nucleic acid construct comprising an HMG-CoA reductase-encoding nucleic acid whose expression in said organism is subject to a reduced regulation, in comparison with the wild type.

(168) A reduced regulation in comparison with the wild type means a reduced regulation and, preferably, no regulation at the expression or protein level, in comparison with the above-defined wild type.

(169) The reduced regulation may be achieved preferably by a promoter which is functionally linked with the coding sequence in the nucleic acid construct and which is subject to a reduced regulation in the organism, in comparison with the wild-type promoter.

(170) For example, the medium ADH promoter in yeast is subject only to a reduced regulation and is therefore particularly preferred as promoter in the above-described nucleic acid construct.

(171) This promoter fragment of the ADH12s promoter, also referred to as ADH1 hereinbelow, exhibits nearly constitutive expression (Ruohonen L, Penttila M, Keranen S. (1991) Optimization of Bacillus -amylase production by Saccharomyces cerevisiae. Yeast. May-June; 7(4):337-462; Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2):147-56) so that transcriptional regulation no longer proceeds via intermediates of ergosterol biosynthesis.

(172) Other preferred promoters with reduced regulation are constitutive promoters such as, for example, the yeast TEF1 promoter, the yeast GPD promoter or the yeast PGK promoter (Mumberg D, Muller R, Funk M. (1995) Yeast vectors for the controlled expression of heterologous proteins in different genetic backgrounds. Gene. 1995 Apr. 14; 156(1):119-22; Chen C Y, Oppermann H, Hitzeman R A. (1984) Homologous versus heterologous gene expression in the yeast, Saccharomyces cerevisiae. Nucleic Acids Res. December 11; 12(23):8951-70).

(173) In a further preferred embodiment, reduced regulation can be achieved by using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid whose expression in the organism is subject to a reduced regulation, in comparison with the orthologous nucleic acid intrinsic to said organism.

(174) Particular preference is given to using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid which encodes only the catalytic region of HMG-CoA reductase (truncated (t-) HMG-CoA reductase). This nucleic acid (t-HMG), described in EP 486 290 and WO 99/16886 encodes only the catalytically active part of HMG-CoA reductase, with the membrane domain responsible for regulation at the protein level missing. This nucleic acid is thus subject to a reduced regulation, in particular in yeast, and leads to an increase in gene expression of HMG-CoA reductase.

(175) In a particularly preferred embodiment, nucleic acids are introduced, preferably via the above-described nucleic acid construct, which encode proteins comprising the amino acid sequence SEQ. ID. NO. 24 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30% identical at the amino acid level to the sequence SEQ ID. NO. 24, and having the enzyme property of an HMG-CoA reductase.

(176) The sequence SEQ ID NO. 24 is the amino acid sequence of the truncated HMG-CoA reductase (t-HMG).

(177) Further examples of HMG-CoA reductases and thus also of the t-HMG-CoA reductases reduced to the catalytic region or of the coding genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or of the corresponding backtranslated nucleic acid sequences from databases with the sequence SEQ ID. No. 24.

(178) Further examples of HMG-CoA reductases and thus also of the t-HMG-CoA reductases reduced to the catalytic region and of the coding genes can furthermore readily be found for various organisms whose genomic sequence is unknown by hybridization techniques and PCR techniques in a manner known per se, for example starting from the sequence SEQ ID NO. 23.

(179) Particular preference is given to using as a truncated HMG-CoA reductase-encoding nucleic acid a nucleic acid comprising the sequence SEQ ID NO. 23.

(180) In a particularly preferred embodiment, the reduced regulation is achieved by using as an HMG-CoA reductase-encoding nucleic acid a nucleic acid whose expression in the organism is subject to a reduced regulation, in comparison with the orthologous nucleic acid intrinsic to said organism, and by using a promoter which is subject to a reduced regulation in said organism, in comparison with the wild-type promoter.

(181) In a preferred embodiment, the lanosterol C14-demethylase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a lanosterol C14-demethylase.

(182) In a further preferred embodiment, gene expression of a nucleic acid encoding a lanosterol C14-demethylase is increased by introducing into the organism one or more nucleic acids encoding a lanosterol C14-demthylase.

(183) For this purpose, it is possible to use in principle any lanosterol C14-demethylase gene (ERG11), i.e. any nucleic acids encoding a lanosterol C14-demethylase. In the case of genomic lanosterol C14-demethylase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate lanosterol C14-demethylase.

(184) Examples of lanosterol C14-demethylase genes are nucleic acids encoding a lanosterol C14-demethylase of Saccharomyces cerevisiae (Kalb V F, Loper J C, Dey C R, Woods C W, Sutter T R (1986) Isolation of a cytochrome P-450 structural gene from Saccharomyces cerevisiae. Gene 45(3):237-45), Candida albicans (Lamb D C, Kelly D E, Baldwin B C, Gozzo F, Boscott P, Richards W G, Kelly S L (1997) Differential inhibition of Candida albicans CYP51 with azole antifungal stereoisomers. FEMS Microbiol Lett 149(1):25-30), Homo sapiens (Stromstedt M, Rozman D, Waterman M R. (1996) The ubiquitously expressed human CYP51 encodes lanosterol 14 -demethylase, a cytochrome P450 whose expression is regulated by oxysterols. Arch Biochem Biophys 1996 May 1; 329(1):73-81c) or Rattus norvegicus, Aoyama Y, Funae Y, Noshiro M, Horiuchi T, Yoshida Y. (1994) Occurrence of a P450 showing high homology to yeast lanosterol 14-demethylase (P450(14DM)) in the rat liver. Biochem Biophys Res Commun. June 30; 201(3):1320-6).

(185) In this preferred embodiment, thus at least one further lanosterol C14-demethylase gene is present in the transgenic organisms of the invention, compared to the wild type.

(186) The number of C14-demethylase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(187) Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 26 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 26, and having the enzyme property of a lanosterol C14-demethylase.

(188) The sequence SEQ. ID. NO. 26 represents the amino acid sequence of Saccharomyces cerevisiae lanosterol C14-demethylase.

(189) Further examples of lanosterol C14-demethylases and lanosterol C14-demethylase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 26.

(190) Further examples of lanosterol C14-demethylases and lanosterol C14-demethylase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 25, by hybridization techniques and PCR techniques in a manner known per se.

(191) Accordingly, a protein which is at least 30% identical at the amino acid level with the sequence SEQ. ID. NO. 26 means a protein which is at least 30% identical when comparing its sequence with the sequence SEQ. ID. NO. 26, in particular according to the above program algorithm with the above set of parameters.

(192) In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae lanosterol C14-demethylase (SEQ. ID. NO. 26).

(193) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(194) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(195) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

(196) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 25 is introduced into the organism.

(197) The sequence SEQ. ID. NO. 25 represents the genomic DNA of Saccharomyces cerevisiae (ORF S0001049), which encodes the lanosterol C14-demethylase of the sequence SEQ ID NO. 26.

(198) Furthermore, all of the lanosterol C14-demethylase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(199) In a preferred embodiment, the squalene-epoxidase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a squalene epoxidase.

(200) In a further preferred embodiment, gene expression of a nucleic acid encoding a squalene epoxidase is increased by introducing into the organism one or more nucleic acids encoding a squalene epoxidase.

(201) For this purpose, it is possible to use in principle any squalene-epoxidase gene (ERG1), i.e. any nucleic acids encoding a squalene epoxidase. In the case of genomic squalene epoxidase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate squalene epoxidase.

(202) Examples of nucleic acids encoding a squalene epoxidase are nucleic acids encoding a squalene epoxidase of Saccharomyces cerevisiae (Jandrositz, A., et al (1991) The gene encoding squalene epoxidase from Saccharomyces cerevisiae: cloning and characterization. Gene 107:155-160, of Mus musculus (Kosuga K, Hata S, Osumi T, Sakakibara J, Ono T. (1995) Nucleotide sequence of a cDNA for mouse squalene epoxidase, Biochim Biophys Acta, February 21; 1260(3):345-8b), of Rattus norvegicus (Sakakibara J, Watanabe R, Kanai Y, Ono T. (1995) Molecular cloning and expression of rat squalene epoxidase. J Biol Chem January 6; 270(1):17-20c) or of Homo sapiens (Nakamura Y, Sakakibara J, Izumi T, Shibata A, Ono T. (1996) Transcriptional regulation of squalene epoxidase by sterols and inhibitors in HeLa cells., J. Biol. Chem. 1996, Apr. 5; 271(14):8053-6).

(203) In this preferred embodiment, thus at least one further squalene epoxidase is present in the transgenic organisms of the invention, compared to the wild type.

(204) The number of squalene-epoxidase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(205) Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 28 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 28, and having the enzyme property of a squalene epoxidase.

(206) The sequence SEQ. ID. NO. 28 represents the amino acid sequence of Saccharomyces cerevisiae squalene epoxidase.

(207) Further examples of squalene epoxidases and squalene-epoxidase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 28.

(208) Further examples of squalene epoxidases and squalene-epoxidase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 27, by hybridization techniques and PCR techniques in a manner known per se.

(209) In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae squalene epoxidase (SEQ. ID. NO. 28).

(210) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(211) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(212) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for backtranslation.

(213) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 27 is introduced into the organism.

(214) The sequence SEQ. ID. NO. 27 represents the genomic DNA of Saccharomyces cerevisiae (ORF YGR175C), which encodes the squalene epoxidase of the sequence SEQ ID NO. 28.

(215) Furthermore, all of the squalene-epoxidase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(216) In a preferred embodiment, the squalene-synthetase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a squalene synthetase.

(217) In a further preferred embodiment, gene expression of a nucleic acid encoding a squalene synthetase is increased by introducing into the organism one or more nucleic acids encoding a squalene synthetase.

(218) For this purpose, it is possible to use in principle any squalene-synthetase gene (ERG9), i.e. any nucleic acids encoding a squalene synthetase. In the case of genomic squalene synthetase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate squalene synthetase.

(219) Examples of nucleic acids encoding a squalene synthetase are nucleic acids encoding a Saccharomyces cerevisiae squalene synthetase (ERG9) (Jennings, S. M., (1991): Molecular cloning and characterization of the yeast gene for squalene synthetase. Proc Natl Acad Sci USA. July 15; 88(14):6038-42), nucleic acids encoding a Botryococcus braunii Okada squalene synthetase (Devarenne, T. P. et al.: Molecular characterization of squalene synthetase from the green microalga Botryococcus braunii, raceB, Arch. Biochem. Biophys. 2000, Jan. 15, 373(2):307-17), nucleic acids encoding a Potato tuber squalene synthetase (Yoshioka H. et al.: cDNA cloning of sesquiter penecyclase and squalene synthase, and expression of the genes in potato tuber infected with Phytophthora infestans, Plant. Cell. Physiol. 1999, September; 40(9):993-8) and nucleic acids encoding a Glycyrrhiza glabra squalene synthetase (Hayashi, H. et al.: Molecular cloning and characterization of two cDNAs for Glycyrrhiza glabra squalene synthase, Biol. Pharm. Bull. 1999, September; 22(9):947-50).

(220) In this preferred embodiment, thus at least one further squalene-synthetase gene is present in the transgenic organisms of the invention, compared to the wild type.

(221) The number of squalene-synthetase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(222) Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 30 or a sequence derived from this sequence by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 30, and having the enzyme property of a squalene synthetase.

(223) The sequence SEQ. ID. NO. 30 represents the amino acid sequence of Saccharomyces cerevisiae squalene synthetase (ERG9).

(224) Further examples of squalene synthetases and squalene-synthetase genes can readily be found, for example, for various organisms hose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 30.

(225) Further examples of squalene synthetases and squalene-synthetase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 29, by hybridization techniques and PCR techniques in a manner known per se.

(226) In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae squalene synthetase (SEQ. ID. NO. 30).

(227) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(228) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(229) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

(230) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 29 is introduced into the organism.

(231) The sequence SEQ. ID. NO. 29 represents the genomic DNA of Saccharomyces cerevisiae (ORF YHR190W), which encodes the squalene synthetase of the sequence SEQ ID NO. 30.

(232) Furthermore, all of the squalene-synthetase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(233) In a preferred embodiment, the sterol-acyltransferase activity is increased compared to the wild type by increasing the gene expression of a nucleic acid encoding a sterol acyltransferase.

(234) In a further preferred embodiment, gene expression of a nucleic acid encoding a sterol acyltransferase is increased by introducing into the organism one or more nucleic acids encoding a sterol acyltransferase.

(235) For this purpose, it is possible to use in principle any sterol-acyltransferase gene (SAT1 or SAT2), i.e. any nucleic acids encoding a sterol acyltransferase.

(236) In the case of genomic sterol acyltransferase nucleic acid sequences from eukaryotic sources, which contain introns, already processed nucleic acid sequences such as the corresponding cDNAs are to be used preferably, if the host organism is unable to or cannot be enabled to express the appropriate sterol acyltransferase.

(237) Examples of nucleic acids encoding a sterol acyltransferase are nucleic acids encoding a Saccharomyces cerevisiae sterol acyltransferase (SAT1) or (SAT2) (Yang, H.: Sterol esterification in yeast: a two-gene process. Science. 1996 May 31; 272(5266):1353-6), a further nucleic acid encoding a further Saccharomyces cerevisiae sterol acyltransferase (J. Biol. Chem. 1996, September 27; 271(39):24157-63), nucleic acids encoding a human sterol acyltransferase (Chang, C. C. et al., Molecular cloning and functional expression of human acyl-coenzyme A:cholesterol acyltransferase cDNA in mutant Chinese hamster ovary cells, J. Biol. Chem. 1993, Oct. 5; 268(28):20747-55) and nucleic acids encoding a murine sterol acyltransferase (Uelmen, P. J.: Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro, J. Biol. Chem. 1995 Nov. 3; 270(44):26192-201).

(238) In this preferred embodiment, thus at least one further sterol-acyltransferase gene is present in the transgenic organisms of the invention, compared to the wild type.

(239) The number of sterol-acyltransferase genes in the transgenic organisms of the invention is at least two, preferably more than two, particularly preferably more than three and very particularly preferably more than five.

(240) Preference is given to using in the above-described method nucleic acids which encode proteins comprising the amino acid sequence SEQ. ID. NO. 32 or SEQ ID NO. 50 or a sequence derived from these sequences by substitution, insertion or deletion of amino acids, which is at least 30%, preferably at least 50%, more preferably at least 70%, still more preferably at least 90%, most preferably at least 95%, identical at the amino acid level with the sequence SEQ. ID. NO. 32 or SEQ. ID. NO. 50, and having the enzyme property of a sterol acyltransferase.

(241) The sequence SEQ. ID. NO. 32 represents the amino acid sequence of Saccharomyces cerevisiae sterol acyltransferase SAT1.

(242) The sequence SEQ. ID. NO. 50 represents the amino acid sequence Saccharomyces cerevisiae sterol acyltransferase SAT2.

(243) SAT 1 and SAT2 differ from one another by a different substrate specificity.

(244) Further examples of sterol acyltransferases and sterol-acyltransferase genes can readily be found, for example, for various organisms whose genomic sequence is known by comparing the homology of the amino acid sequences or the corresponding backtranslated nucleic acid sequences from databases with the SeQ ID. NO. 32 or 50.

(245) Further examples of sterol acyltransferase and sterol-acyltransferase genes can furthermore readily be found for various organisms whose genomic sequence is unknown, for example starting from the sequence SEQ. ID. No. 31 or 49, by hybridization techniques and PCR techniques in a manner known per se.

(246) In another preferred embodiment, nucleic acids are introduced into organisms, which encode proteins comprising the amino acid sequence of Saccharomyces cerevisiae sterol acyltransferase SAT1 (SEQ. ID. NO. 32) or Saccharomyces cerevisiae sterol acyltransferase SAT2 (SEQ. ID. NO. 50).

(247) Suitable nucleic acid sequences can be obtained, for example, by backtranslating the polypeptide sequence according to the genetic code.

(248) Preference is given to using for this those codons which are frequently used according to the organism-specific codon usage. Said codon usage can readily be determined on the basis of computer analyses of other known genes of the organisms in question.

(249) If the protein is to be expressed in yeast, for example, it is often advantageous to use the codon usage of yeast for the backtranslation.

(250) In a particularly preferred embodiment, a nucleic acid comprising the sequence SEQ. ID. NO. 31 or 49 is introduced into the organism.

(251) The sequence SEQ. ID. NO. 31 represents the genomic DNA of Saccharomyces cerevisiae (ORF YNR019W), which encodes the sterol acyltransferase SAT1 of the sequence SEQ ID NO. 32.

(252) The sequence SEQ. ID. NO. 49 represents the genomic DNA of Saccharomyces cerevisiae (ORF YCR048W), which encodes the sterol acyltransferase SAT2 of the sequence SEQ ID NO. 50.

(253) Furthermore, all of the sterol-acyltransferase genes mentioned above can be prepared in a manner known per se by chemical synthesis from the nucleotide building blocks, for example by fragment condensation of individual overlapping complementary nucleic acid building blocks of the double helix. The chemical synthesis of oligonucleotides may be carried out, for example, in a known manner according to the phosphoramidite method (Voet, Voet, 2nd edition, Wiley Press New York, pages 896-897). Annealing of synthetic oligonucleotides and filling-in of gaps with the aid of the Klenow fragment of DNA polymerase and the ligation reactions and also general cloning methods are described in Sambrook et al. (1989), Molecular cloning: A laboratory manual, Cold Spring Harbor Laboratory Press.

(254) According to the invention, organisms mean, for example, bacteria, in particular bacteria of the genus Bacillus, Escherichia coli, Lactobacillus spec. or Streptomyces spec.,

(255) for example yeasts, in particular yeasts of the genus Saccharomyces cerecisiae, Pichia pastoris or Klyveromyces spec.

(256) for example fungi, in particular fungi of the genus Aspergillus spec., Penicillium spec. or Dictyostelium spec.

(257) and also, for example, insect cell lines, which are capable, either as wild type or owing to previous genetic modification, of producing zymosterol and/or the biosynthetic intermediates and/or secondary products thereof.

(258) Particularly preferred organisms are yeasts, in particular those of the species Saccharomyces cerevisiae, in particular the yeast strains Saccharomyces cerevisiae AH22, Saccharomyces cerevisiae GRF, Saccharomyces cerevisiae DBY747 and Saccharomyces cerevisiae BY4741.

(259) In the case of yeasts as organisms or genetically modified organisms, it is possible, as mentioned above, to increase at least one of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity by overexpressing the corresponding nucleic acids.

(260) The overexpression may be carried out both homologously by introducing nucleic acids intrinsic to yeast and heterologously by introducing nucleic acids from other organisms, in particular mammals, or natural or artificial variants derived therefrom into the yeast. Preference is given to using mammalian genes in yeasts, since these genes have a better substrate specificity with respect to 7-dehydrocholesterol.

(261) The 8-7-isomerase activity, 5-desaturase activity, 24-reductase activity, C24-methyltransferase activity, 22-desaturase activity, HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity of the genetically modified organism of the invention and of the reference organism is determined under the following conditions:

(262) The activity of HMG-CoA reductase is determined as described in Th. Polakowski, Molekularbiologische Beeinflussung des Ergosterolstoffwechsels der Hefe Saccharomyces cerevisiae [influencing the ergosterol metabolism of the yeast Saccharomyces cerevisiae by molecular biological means], Shaker-Verlag, Aachen 1999, ISBN 3-8265-6211-9, beschrieben.

(263) According to this, 10.sup.9 yeast cells of a 48 h culture are harvested by centrifugation (3500.times.g, 5 min) and washed in 2 ml of buffer I (100 mM potassium phosphate buffer, pH 7.0). The cell pellet is taken up in 500 l of buffer 1 (cytosolic proteins) or 2 (100 mM potassium phosphate buffer pH 7.0; 1% Triton X-100) (total proteins), and 1 l of 500 mM PMSF in isopropanol is added. 500 l of glass beads (d=0.5 mm) are added to the cells and the cells are disrupted by vortexing 5.times. for one minute each. The liquid between the glass beads is transferred to a new Eppendorf vessel. Cell debris and membrane components are removed by centrifugation (14000.times.g; 15 min).

(264) The supernatant is transferred to a new Eppendorf vessel and represents the protein fraction.

(265) The activity of HMG-CoA reductase is determined by measuring NADPH+H.sup.+ consumption during the reduction of 3-hydroxy-3-methylglutaryl-CoA which is added as substrate.

(266) In a 1000 l assay mixture, 20 l of yeast protein isolate are combined with 910 l of buffer I; 50 l of 0.1 M DTT and 10 l of 16 mM NADPH+H.sup.+. The mixture is adjusted to 30.degree. C. and measured in a spectrophotometer at 340 nm for 7.5 min. The decrease in NADPH, which is measured over this period, is the rate of degradation without addition of substrate and is taken into account as background.

(267) Subsequently, substrate (10 l of 30 mM HMG-CoA) is added, and measurement continues for another 7.5 min. The HMG-CoA-reductase activity is calculated by determining the specific rate of NADPH degradation.

(268) The activity of lanosterol C14-demethylase is determined as described in Omura, T and Sato, R. (1964) The carbon monoxide binding pigment in liver microsomes. J. Biol. Chem. 239, 2370-2378. In this assay, the amount of P450 enzyme as holoenzyme with bound heme can be semi-quantified. The (active) holoenzyme (with heme) can be reduced by CO and only the CO-reduced enzyme has an absorption maximum at 450 nm. Thus the absorption maximum at 450 nm is a measure for lanosterol C14-demethylase activity.

(269) The activity is determined by diluting a microsomal fraction (4-10 mg/ml protein in 100 mM potassium phosphate buffer) 1:4 so that the protein concentration used in the assay is 2 mg/ml. The assay is carried out directly in a cuvette.

(270) A spatula tipful of dithionite (S.sub.2O.sub.4Na.sub.2) is added to the microsomes. The baseline is recorded in the 380-500 nm region in a spectrophotometer.

(271) Subsequently, approx. 20-30 CO bubbles are passed through the sample. The absorption is then measured in the same region. The absorption level at 450 nm corresponds to the amount of P450 enzyme in the assay mixture.

(272) The activity of squalene epoxidase is determined as described in Leber R, Landl K, Zinser E, Ahorn H, Spok A, Kohlwein S D, Turnowsky F, Daum G. (1998) Dual localization of squalene epoxidase, Erg1p, in yeast reflects a relationship between the endoplasmic reticulum and lipid particles, Mol. Biol. Cell. 1998, February; 9(2):375-86.

(273) In this method, a total volume of 500 l contains from 0.35 to 0.7 mg of microsomal protein or from 3.5 to 75 g of lipid-particle protein in 100 mM Tris-HCl, pH 7.5, 1 mM EDTA, 0.1 mM FAD, 3 mM NADPH, 0.1 mM squalene 2,3-epoxidase cyclase inhibitor U18666A, 32 M [.sup.3H]squalene dispersed in 0.005% Tween 80.

(274) The assay is carried out at 30.degree. C. After 10 minutes of pretreatment, the reaction is started by adding squalene and stopped after 15, 30 or 45 min by lipid extraction with 3 ml of chloroform/methanol (2:1 vol/vol) and 750 l of 0.035% MgCl.sub.2.

(275) The lipids are dried under nitrogen and redissolved in 0.5 ml of chloroform/methanol (2:1 vol/vol). For thin layer chromatography, portions are applied to a Silica Gel 60 late (0.2 mm) and fractionated using chloroform as eluent. The positions containing [.sup.3H]2,3-oxidosqualene and [.sup.3H]squalene were scraped off and quantified in a scintillation counter.

(276) The 8-7-isomerase activity is determined, with a slight modification, as described in Silve S. et al.: Emopamil-binding Protein, a Mammalian Protein That Binds a Series of Structurally Diverse Neuroprotective Agents, Exhibits 8-7 Sterol Isomerase Activity in Yeast. J Biol Chem 1996 Sep. 13; 271(37):22434-40:

(277) Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 M cholesta-8-en-3-ol at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

(278) The 5-desaturase activity is determined, with slight modification, as described in Nishi, S. et al. (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. Acta1490(1-2),106-108:

(279) Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 M lathosterol and 2 mM NADH at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

(280) The 24-reductase activity can be determined as described below:

(281) Microsomes prepared from a culture volume of 10 ml are incubated in the presence of 75 M cholesta-5,7,24-trienol at 30.degree. C. for 3 h. The sterols are then extracted with 4 times 5 ml of hexane and purified. Aliquots are analyzed by means of GC/MS.

(282) The C24-methyltransferase activity can be determined as described below:

(283) 80% of the protein Erg6p (C24-methyltransferase) are detectable in lipid particles in the yeast (Athenstaedt K, Zweytick D, Jandrositz A, Kohlwein S D, Daum G: Identification and characterization of major lipid particle proteins of the yeast Saccharomyces cerevisiae. J. Bacteriol. 1999 October; 181(20):6441-8). The enzyme activity is determined by preparing lipid particles from a culture volume (48 h) of 100 ml (according to a method described in Athenstaedt K, Zweytick D, Jandrositz A, Kohlwein S D, Daum G: Identification and characterization of major lipid particle proteins of the yeast Saccharomyces cerevisiae. J. Bacteriol. 1999 October; 181(20):6441-8).

(284) The protein content is determined by a Biorad enzyme assay and 3 mg of protein are used in a volume of 500 l for each assay mixture. 50 M [methyl-.sup.3H.sub.3]-S-adenosylmethionine and 50 M zymosterol are added to the assay mixture which is then incubated at 35.degree. C. for 10 min. Subsequently, the same volume (500 l) of chloroform/methanol (4:1) is added and the sterols are then extracted.

(285) The proportion of zymosterol with incorporated [methyl-.sup.3H.sub.3]-S-adenosylmethionine can be determined by means of scintillation measurement, since chloroform/methanol extraction extracts only lipid-soluble substances. For quantification, the radioactive decays are likewise determined for 50 M [methyl-.sup.3H.sub.3]-S-adenosylmethionine by means of scintillation measurement.

(286) This method is a modification of the method described in Nes W D, Guo D, Zhou W.: Substrate-based inhibitors of the (S)-adenosyl-L-methionine:24(25)-to 24(28)-sterol methyl transferase from Saccharomyces cerevisiae, Arch. Biochem. Biophys. 1997 Jun. 1; 342(1):68-81.

(287) The activity of 22-desaturase (ERG5p) can be determined as described below:

(288) Various concentrations of Ergosta-5,7-dienol, purified from S. cerevisiae erg5 mutants (Parks et al, 1985. Yeast sterols.yeast mutants as tools for the study of sterol metabolism. Methods Enzymol. 111:333-346) and 50 g of dilauroylphosphatidylcholine are mixed and treated with ultrasound until a white suspension is formed. Prepared microsomes are added (1 ml)(3 mg/ml protein). NADPH (1 mM final concentration) is added to the assay mixture to start the enzyme reaction. The mixture is incubated at 37.degree. C. for 20 min. The reaction is stopped by adding 3 ml of methanol and sterols are hydrolyzed by adding 2 ml of 60% (wt/vol) KOH in water. The mixture is incubated at 90.degree. C. for 2 h. After cooling, the mixture is extracted three times with 5 ml of hexane and concentrated in a rotary evaporator. Subsequently, the sterols are silylated with bis(trimethylsilyl)trifluoroacetamide (50 l in 50 l toluene) at 60.degree. C. for 1 h. The sterols are analyzed by gas chromatography-mass spectrometry (GC-MS) (for example Model VG 12-250 gas chromatograph-mass spectrometer; VG Biotech, Manchester, United Kingdom). The resultant 22-desaturated intermediate can be identified depending on the amount of substrate used. Microsomes which are not incubated with substrate serve as reference.

(289) This method is a modification of the method described in Lamb et al: Purification, reconstitution, and inhibition of cytochrome P-450 sterol 22-desaturase from the pathogenic fungus Candida glabrata. Antimicrob Agents Chemother. 1999 July; 43(7):1725-8.

(290) The squalene-synthetase activity can be determined as described below:

(291) The assays contain 50 mM MOPS, pH 7.2, 10 mM MgCl.sub.2, 1% (v/v) Tween-80, 10% (v/v) 2-propanol, 1 mM DTT, 1 mg/mL BSA, NADPH, FPP (or PSPP) and microsomes (protein content 3 mg) in a total volume of 200 l in glass tubes. The reaction mixtures containing the radioactive substrate [1-.sup.3H]FPP (15-30 mCi/mol) are incubated at 30.degree. C. for 30 min and one volume of 1:1 (v/v) 40% aqueous KOH:methanol is added to the suspension mixture. Liquid NaCl is added to saturate the solution and 2 ml of naphtha containing 0.5% (v/v) squalene are likewise added.

(292) The suspension is vortexed for 30 s. In each case 1 ml of the naphtha layer is applied to a packed 0.5.times.6 cm aluminum column (80-200 mesh, Fisher) using a Pasteur pipette. The column has been pre-equilibrated with 2 ml of naphtha containing 0.5% (v/v) squalene. The column is then eluted with 5.times.1 ml of toluene containing 0.5% (v/v) squalene. Squalene radioactivity is measured in Cytoscint (ICN) scintillation cocktail in a scintillation counter (Beckman).

(293) This method is a modification of the method described in Radisky et al., Biochemistry. 2000 Feb. 22; 39(7):1748-60, Zhang et al. (1993) Arch. Biochem. Biophys. 304, 133-143 and Poulter, C. D. et al. (1989) J. Am. Chem. Soc. 111, 3734-3739.

(294) The sterol-acyltransferase activity can be determined as described below:

(295) A 200 ml main culture is inoculated at 1% strength from a 20 ml preculture which has been incubated for two days and is incubated in complete medium overnight. The cells are harvested and then washed in two volumes of HP buffer (100 mM potassium phosphate buffer, pH 7.4; 0.5 mM EDTA; 1 mM glutathione; 20 M leupeptin; 64 M benzamidine; 2 mM PMSF) and resuspended in HP buffer.

(296) After adding 1 g of glass beads, the cells are disrupted by vortexing 8 times for one minute each. The supernatant is ultracentrifuged at 105000.times.g. The pellet is taken up in 1 ml of ACAT buffer (100 mM potassium phosphate buffer pH7,4; 1 mM glutathione).

(297) The enzyme assay is carried out in a volume of 500 l. The substrate ergosterol is taken up in 62.5 ml of 0.5.times.ACAT buffer with vigorous vortexing. 250 l of this solution are used as substrate in the assay. To this, 20 l of protein extract, 50 l of water and 130 l of 0.5.times.ACAT buffer are added.

(298) The mixture is incubated at 37.degree. C. for 15 min. Subsequently, 50 l of 14C-oleoyl-CoA (600000 dpm) are added and the reaction is stopped after one minute by adding 4 ml of chloroform/methanol (2:1). To this, 500 l of H.sub.2O are added. The phases are separated by briefly centrifuging the suspension at 2000.times.g. The lower phase is evaporated to dryness in a pear-shaped flask and redissolved in 100 l of chloroform/methanol (4:1) and applied to a TLC plate (silica gel 60 F254). The TLC is carried out using petroleum ether/diethyl ether/acetic acid 90:10:1 as eluent. The spots of the steryl ester fractions are cut out and the number of radioactive decays is determined in a scintillation column. The enzyme activity can be determined via the amount of sterile ester-bound 14C-oleoyl-CoA molecules.

(299) In a preferred embodiment of the method of the invention 7-dehydrocholesterol and/or the biosynthetic intermediates and/or intermediates thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type, an increased activity of at least one of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity and which have additionally a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and 22-desaturase activity and which have additionally an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased squalene-epoxidase activity.

(300) In other preferred embodiments of the method of the invention, 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type,

(301) an increased 8-7-isomerase activity,

(302) an increased 5-desaturase activity,

(303) an increased 24-reductase activity,

(304) an increased 8-7-isomerase activity and an increased 5-desaturase activity,

(305) an increased 8-7-isomerase activity and an increased 24-reductase activity,

(306) an increased 5-desaturase activity and an increased 24-reductase activity, an increased 8-7-isomerase activity, an increased 5-desaturase activity and an increased 24-reductase activity,

(307) an increased 8-7-isomerase activity and a reduced C24-methyltransferase activity,

(308) an increased 5-desaturase activity and a reduced C24-methyltransferase activity,

(309) an increased 24-reductase activity and a reduced C24-methyltransferase activity,

(310) an increased 8-7-isomerase activity, an increased 5-desaturase activity and a reduced C24-methyltransferase activity,

(311) an increased 8-7-isomerase activity, an increased 24-reductase activity and a reduced C24-methyltransferase activity,

(312) an increased 5-desaturase activity, an increased 24-reductase activity and a reduced C24-methyltransferase activity,

(313) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity and a reduced C24-methyltransferase activity,

(314) an increased 8-7-isomerase activity and a reduced 22-desaturase activity,

(315) an increased 5-desaturase activity and a reduced 22-desaturase activity,

(316) an increased 24-reductase activity and a reduced 22-desaturase activity,

(317) an increased 8-7-isomerase activity, an increased 5-desaturase activity and a reduced 22-desaturase activity,

(318) an increased 8-7-isomerase activity, an increased 24-reductase activity and a reduced 22-desaturase activity,

(319) an increased 5-desaturase activity, an increased 24-reductase activity and a reduced 22-desaturase activity,

(320) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity and a reduced 22-desaturase activity,

(321) an increased 8-7-isomerase activity, a reduced 22-desaturase activity and a reduced C24-ethyltransferase activity,

(322) an increased 5-desaturase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(323) an increased 24-reductase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(324) an increased 8-7-isomerase activity, an increased 5-desaturase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(325) an increased 8-7-isomerase activity, an increased 24-reductase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(326) an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(327) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity and a reduced C24-methyltransferase activity,

(328) an increased 8-7-isomerase activity and an increased HMG-CoA-reductase activity,

(329) an increased 5-desaturase activity and an increased HMG-CoA-reductase activity,

(330) an increased 24-reductase activity and an increased HMG-CoA-reductase activity,

(331) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity and an increased 5-desaturase activity,

(332) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity and an increased 24-reductase activity,

(333) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity and an increased 24-reductase activity,

(334) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased HMG-CoA-reductase activity and an increased 24-reductase activity,

(335) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(336) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(337) an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(338) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(339) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(340) an increased 5-desaturase activity, an increased 24-reductase activity and a reduced C24-methyltransferase activity,

(341) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(342) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(343) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(344) an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(345) an increased 8-7-isomerase activity, an increased 5-desaturase

(346) activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(347) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(348) an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(349) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(350) an increased 8-7-isomerase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(351) an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(352) an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(353) an increased 8-7-isomerase activity, an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(354) an increased 8-7-isomerase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(355) an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(356) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity and a reduced C24-methyltransferase activity,

(357) an increased 8-7-isomerase activity and an increased lanosterol-C14-demethylase activity,

(358) an increased 5-desaturase activity and an increased lanosterol-C14-demethylase activity,

(359) an increased 24-reductase activity and an increased lanosterol-C14-demethylase activity,

(360) an increased 8-7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased 5-desaturase activity,

(361) an increased 8-7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(362) an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(363) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(364) an increased 8-7-isomerase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(365) an increased 5-desaturase activity and a reduced C24-methyltransferase activity,

(366) an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(367) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(368) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(369) an increased 5-desaturase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(370) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(371) an increased 8-7-isomerase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(372) an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(373) an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(374) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(375) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(376) an increased 5-desaturase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(377) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(378) an increased 8-7-isomerase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(379) an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(380) an increased 24-reductase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(381) an increased 8-7-isomerase activity, an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(382) an increased 8-7-isomerase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(383) an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(384) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(385) an increased 8-7-isomerase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity,

(386) an increased 5-desaturase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity,

(387) an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and an increased HMG-CoA-reductase activity,

(388) an increased AB-A7-isom erase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased 5-desaturase activity,

(389) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(390) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(391) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased 24-reductase activity,

(392) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(393) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(394) an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(395) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(396) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(397) an increased 5-desaturase activity, an increased 24-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(398) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity,

(399) an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(400) an increased 8-7-isomerase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(401) an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(402) an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(403) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(404) an increased 8-7-isomerase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(405) an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity and a reduced 22-desaturase activity,

(406) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced 22-desaturase activity,

(407) an increased 8-7-isomerase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(408) an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(409) an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(410) an increased 8-7-isomerase activity, an increased 5-desaturase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(411) an increased 8-7-isomerase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(412) an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(413) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(414) an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(415) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(416) an increased lanosterol-C14-demethylase activity and a reduced C24-methyltransferase activity,

(417) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(418) an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity, or

(419) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity.

(420) In further particularly preferred embodiments of the method of the invention, 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are prepared by culturing organisms, in particular yeasts, which have, compared to the wild type, an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity and an increased squalene-epoxidase activity,

(421) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity,

(422) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(423) an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity and a reduced C24-methyltransferase activity,

(424) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(425) an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased squalene-synthetase activity and a reduced C24-methyltransferase activity, an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity,

(426) an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased sterol-acyltransferase activity and a reduced C24-methyltransferase activity,

(427) an increased 8-7-isomerase activity, an increased 5-desaturase activity, an increased 24-reductase activity, a reduced 22-desaturase activity, an increased HMG-CoA-reductase activity, an increased lanosterol-C14-demethylase activity, an increased squalene-epoxidase activity, an increased squalene-synthetase activity, an increased sterol-acyltransferase activity and a reduced C24-methyltransferase activity.

(428) Biosynthetic 7-dehydrocholesterol intermediates mean all compounds which appear as intermediates during 7-dehydrocholesterol biosynthesis in the organism used, preferably the compounds mevalonate, farnesyl pyrophosphate, geraniol pyrophosphate, squalene epoxide, 4-dimethylcholesta-8,14,24-trienol, 4,4-dimethylzymosterol, squalene, farnesol, geraniol, lanosterol, zymosterol, lathosterol, cholesta-7,24-dienol and cholesta-5,7,24-trienol.

(429) Biosynthetic secondary products of zymosterol mean all compounds which can be derived biosynthetically from 7-dehydrocholesterol in the organism used, i.e. for which 7-dehydrocholesterol appears as an intermediate. These may be compounds which the organism used produces naturally from 7-dehydrocholesterol, such as, for example, cholesterol or vitamin D.sub.3 in mammals. However, they also mean compounds which can be produced in the organism from 7-dehydrocholesterol only by introducing genes and enzyme activities of other organisms for which the starting organism has no orthologous gene.

(430) It is possible, for example, to prepare secondary products from 7-dehydrocholesterol, which are naturally present only in mammals, by introducing mammalian genes into yeast:

(431) Introducing a human or murine nucleic acid encoding a human or murine -7-reductase enables the yeast to produce cholesterol.

(432) Under UV irradiation, vitamin D.sub.3 (cholecalciferol) is produced from 7-dehydrocholesterol via provitamin D.sub.3 by rearrangement.

(433) Therefore, the biosynthetic secondary products of 7-dehydrocholesterol mean in particular provitamin D3, vitamin D.sub.3 (cholecalciferol) and/or cholesterol.

(434) Preferred biosynthetic secondary products are provitamin D.sub.3 and in particular vitamin D.sub.3.

(435) The compounds prepared in the method of the invention may be used in biotransformations, chemical reactions and for therapeutic purposes, for example for producing vitamin D.sub.3 from 7-dehydrocholesterol via UV irradiation, or for producing steroid hormones via biotransformation starting from cholesta-7,24-dienol or cholesta-5,7,24-trienol.

(436) In the inventive method for preparing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof, the step of culturing the genetically modified organisms, also referred to as transgenic organisms hereinbelow, is preferably followed by harvesting said organisms and isolating 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof from said organisms.

(437) The organisms are harvested in a manner known per se and appropriate for the particular organism. Microorganisms such as bacteria, mosses, yeasts and fungi or plant cells which are cultured in liquid media by fermentation may be removed, for example, by centrifugation, decanting or filtration.

(438) 7-Dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof are isolated from the harvested biomass together or each compound is harvested separately in a manner known per se, for example by extraction and, where appropriate, further chemical or physical purification processes such as, for example, precipitation methods, crystallography, thermal separation methods such as rectification methods or physical separation methods such as, for example, chromatography.

(439) The transgenic organisms, in particular yeasts, are preferably prepared either by transforming the starting organisms, in particular yeasts, with a nucleic acid construct containing at least one nucleic acid selected from the group consisting of nucleic acids encoding a 8-7-isomerase, nucleic acids encoding a 5-desaturase and nucleic acids encoding a 24-reductase which are functionally linked with one or more regulatory signals ensuring transcription and translation in organisms. In this embodiment, the transgenic organisms are prepared using a nucleic acid construct.

(440) In a particularly preferred embodiment, the above-described nucleic acid construct additionally contains at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

(441) However, the transgenic organisms may also preferably be prepared by transforming the starting organisms, in particular yeasts, with at least one nucleic acid construct selected from the group consisting of nucleic acid constructs containing nucleic acids encoding a 8-7-isomerase, nucleic acid construct containing nucleic acids encoding a 5-desaturase and nucleic acid construct containing nucleic acids encoding a 24-reductase which nucleic acids are in each case functionally linked to one or more regulatory signals ensuring transcription and translation in organisms. In this embodiment, the transgenic organisms are prepared using individual nucleic acid constructs or a combination of nucleic acid constructs.

(442) In a particularly preferred embodiment, the above-described combination of nucleic acid constructs additionally comprises at least one nucleic acid construct selected from the group consisting of nucleic acid construct containing nucleic acids encoding an HMG-CoA-reductase activity, nucleic acid construct containing nucleic acids encoding a lanosterol-C14-demethylase, nucleic acid construct containing nucleic acids encoding a squalene epoxidase, nucleic acid construct containing nucleic acids encoding a squalene synthetase and nucleic acid construct containing nucleic acids encoding a sterol acyltransferase which nucleic acids are in each case functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

(443) Nucleic acid constructs in which the encoding nucleic acid sequence is functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, in particular in yeasts, are also referred to as expression cassettes hereinbelow.

(444) Examples of nucleic acid constructs containing said expression cassette are vectors and plasmids.

(445) Accordingly, the invention further relates to nucleic acid constructs, in particular nucleic acid constructs functioning as expression cassettes, which contain at least one nucleic acid selected from the group consisting of nucleic acids encoding a 8-7-isomerase, nucleic acids encoding a 5-desaturase and nucleic acids encoding a 24-reductase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

(446) In a preferred embodiment, said nucleic acid construct additionally comprises at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

(447) As an alternative, it is also possible to prepare the transgenic organisms of the invention by transformation with individual nucleic acid constructs or with a combination of nucleic acid constructs, said combination comprising at least one nucleic acid construct selected from the groups A to C

(448) A nucleic acid construct comprising nucleic acids encoding a 8-7-isomerase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms,

(449) B nucleic acid construct comprising nucleic acids encoding a 5-desaturase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms and

(450) C nucleic acid construct comprising nucleic acids encoding a 24-reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, and at least one nucleic acid construct selected from the groups D to H

(451) D nucleic acid construct comprising nucleic acids encoding an HMG-CoA reductase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, E nucleic acid construct comprising nucleic acids encoding a lanosterol C14-demethylase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, F nucleic acid construct comprising nucleic acids encoding a squalene epoxidase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, G nucleic acid construct comprising nucleic acids encoding a squalene synthetase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms, H nucleic acid construct comprising nucleic acids encoding a sterol acyltransferase, which are functionally linked to one or more regulatory signals ensuring transcription and translation in organisms.

(452) The regulatory signals preferably contain one or more promoters which ensure transcription and translation in organisms, in particular in yeasts.

(453) The expression cassettes include regulatory signals, i.e. regulatory nucleic acid sequences, which control expression of the coding sequence in the host cell. According to a preferred embodiment, an expression cassette comprises upstream, i.e. at the 5 end of the coding sequence, a promoter and downstream, i.e. at the 3 end, a terminator and, where appropriate, further regulatory elements which are operatively linked to the coding sequence for at least one of the above-described genes located in between.

(454) Operative linkage means the sequential arrangement of promoter, coding sequence, where appropriate, terminator and, where appropriate, further regulatory elements in such a way that each of the regulatory elements can properly carry out its function in the expression of the coding sequence.

(455) The preferred nucleic acid constructs, expression cassettes and plasmids for yeasts and fungi and methods for preparing transgenic yeasts and also the transgenic yeasts themselves are described by way of example below.

(456) A suitable promoter of the expression cassette is in principle any promoter which is able to control the expression of foreign genes in organisms, in particular in yeasts.

(457) Preference is given to using in particular a promoter which is subject to reduced regulation in yeast, such as, for example, the medium ADH promoter.

(458) This promoter fragment of the ADH12s promoter, also referred to as ADH1 hereinbelow, exhibits nearly constitutive expression (Ruohonen L, Penttila M, Keranen S. (1991) Optimization of Bacillus -amylase production by Saccharomyces cerevisiae. Yeast. May-June; 7(4):337-462; Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2):147-56) so that transcriptional regulation no longer proceeds via intermediates of ergosterol biosynthesis.

(459) Other preferred promoters with reduced regulation are constitutive promoters such as, for example, the yeast TEF1 promoter, the yeast GPD promoter or the yeast PGK promoter (Mumberg D, Muller R, Funk M. (1995) Yeast vectors for the controlled expression of heterologous proteins in different genetic backgrounds. Gene. 1995 Apr. 14; 156(1):119-22; Chen C Y, Oppermann H, Hitzeman R A. (1984) Homologous versus heterologous gene expression in the yeast, Saccharomyces cerevisiae. Nucleic Acids Res. December 11; 12(23):8951-70).

(460) The expression cassette may also contain inducible promoters, in articular a chemically inducible promoter which can be used to control expression of the nucleic acids encoding a 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA-reductase, lanosterol-C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase in the organism at a particular time.

(461) Promoters of this kind, such as, for example, the yeast Cupl promoter (Etcheverry T. (1990) Induced expression using yeast copper metallothionein promoter. Methods Enzymol. 1990; 185:319-29.), the yeast Gall-10 promoter (Ronicke V, Graulich W, Mumberg D, Muller R, Funk M. (1997) Use of conditional promoters for expression of heterologous proteins in Saccharomyces cerevisiae, Methods Enzymol. 283:313-22) or the yeast Pho5 promoter (Bajwa W, Rudolph H, Hinnen A. (1987) PHO5 upstream sequences confer phosphate control on the constitutive PHO3 gene. Yeast. 1987 March; 3(1):33-42), may be used, for example.

(462) A suitable terminator of the expression cassette is in principle any terminator which is able to control the expression of foreign genes in organisms, in particular in yeasts.

(463) Preference is given to the tryptophan terminator of yeasts (TRP1 terminator).

(464) An expression cassette is preferably prepared by fusing a suitable promoter with the above-described nucleic acids encoding a 8-7-isomerase, 5-desaturase, 24-reductase, HMG-CoA-reductase, lanosterol-C14-demethylase, squalene epoxidase, squalene synthetase or sterol acyltransferase and, where appropriate, a terminator according to common recombination and cloning techniques as described, for example, in T. Maniatis, E. F. Fritsch and J. Sambrook, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1989) and in T. J. Silhavy, M. L. Berman and L. W. Enquist, Experiments with Gene Fusions, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1984) and in Ausubel, F. M. et al., Current Protocols in Molecular Biology, Greene Publishing Assoc. and Wiley-Interscience (1987).

(465) The nucleic acids of the invention may be prepared synthetically or obtained naturally or may contain a mixture of synthetic and natural nucleic acid components and may also comprise various heterologous gene sections of various organisms.

(466) As described above, preference is given to synthetic nucleotide sequences with codons which are preferred by yeasts. These codons which are preferred by yeasts may be determined from codons which have the highest frequency in proteins and which are expressed in most of the interesting yeast species.

(467) When preparing an expression cassette, it is possible to manipulate various DNA fragments in order to obtain a nucleotide sequence which expediently can be read in the correct direction and is provided with a correct reading frame. The DNA fragments may be linked to one another by attaching adaptors or linkers to said fragments.

(468) Expediently, the promoter and terminator regions may be provided in the direction of transcription with a linker or polylinker which contains one or more restriction sites for inserting this sequence. Normally, the linker has from 1 to 10, mostly from 1 to 8, preferably from 2 to 6, restriction sites. Generally, the linker is, within the regulatory regions, less than 100 bp, frequently less than 60 bp, but at least 5 bp, in length. The promoter may be both native or homologous and non-native or heterologous to the host organism. The expression cassette preferably includes in the 5-3 direction of transcription the promoter, a coding nucleic acid sequence or a nucleic acid construct and a region for transcriptional termination. Various termination regions can be exchanged with one another randomly.

(469) It is furthermore possible to use manipulations which provide appropriate restriction cleavage sites or which remove excess DNA or restriction cleavage sites. In those cases for which insertions, deletions or substitutions such as, for example, transitions and transversions are suitable, in vitro mutagenesis, primer repair, restriction or ligation can be used.

(470) In suitable manipulations such as, for example, restriction, chewing-back or filling-in of protruding ends to form blunt ends, complementary fragment ends may be provided for ligation.

(471) The invention further relates to the use of the above-described nucleic acids, the above-described nucleic acid constructs or the above-described proteins for preparing transgenic organisms, in particular yeasts.

(472) Preferably, said transgenic organisms, in particular yeasts, have an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof compared to the wild type.

(473) Therefore, the invention further relates to the use of the above-described nucleic acids or the nucleic acid constructs of the invention for increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof in organisms.

(474) The above-described proteins and nucleic acids may be used for producing 7-dehydrocholesterol and/or the biosynthetic intermediates and/or secondary products thereof in transgenic organisms.

(475) The transfer of foreign genes into the genome of an organism, in particular of yeast, is referred to as transformation.

(476) For this purpose, methods known per se can be used for transformation, in particular in yeasts.

(477) Examples of suitable methods for transforming yeasts are the LiAC method as described in Schiestl R H, Gietz R D. (1989) High efficiency transformation of intact yeast cells using single stranded nucleic acids as a carrier, Curr Genet. December; 16 (5-6):339-46, electroporation as described in Manivasakam P, Schiestl R H. (1993) High efficiency transformation of Saccharomyces cerevisiae by electroporation. Nucleic Acids Res. September 11; 21(18):4414-5, and the preparation of protoplasts, as described in Morgan A J. (1983) Yeast strain improvement by protoplast fusion and transformation, Experientia Suppl. 46:155-66

(478) The construct to be expressed is preferably cloned into a vector, in particular into plasmids which are suitable for transforming yeasts, such as, for example, the vector systems Yep24 (Naumovski L, Friedberg E C (1982) Molecular cloning of eucaryotic genes required for excision repair of UV-irradiated DNA: isolation and partial characterization of the RAD.sub.3 gene of Saccharomyces cerevisiae. J Bacteriol October; 152(1):323-31), Yep13 (Broach J R, Strathern J N, Hicks J B. (1979) Transformation in yeast: development of a hybrid cloning vector and isolation of the CAN1 gene. Gene. 1979 December; 8(1):121-33), the pRS series of vectors (Centromer and Episomal) (Sikorski R S, Hieter P. (1989) A system of shuttle vectors and yeast host strains designed for efficient manipulation of DNA in Saccharomyces cerevisiae. Genetics. May; 122(1):19-27) and the vector systems YCp19 or pYEXBX.

(479) Accordingly, the invention furthermore relates to vectors, in particular plasmids, which comprise the above-described nucleic acids, nucleic acid constructs or expression cassettes.

(480) The invention further relates to a method for preparing genetically modified organisms by functionally introducing an above-described nucleic acid or an above-described nucleic acid construct into the starting organism.

(481) The invention further relates to said genetically modified organisms, the genetic modification increasing at least one of the activities selected from the group consisting of 8-7-isomerase activity, 5-desaturase activity and 24-reductase activity, compared to a wild type.

(482) Preferably, at least one of the activities is increased by increasing the gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a 8-7-isomerase, nucleic acids encoding a 5-desaturase and nucleic acids encoding a 24-reductase.

(483) Preferably, gene expression of the above-described nucleic acids is increased by increasing in the organism the copy number of the nucleic acids encoding a 8-7-isomerase, encoding a 5-desaturase and/or encoding a 24-reductase.

(484) Accordingly, the invention preferably relates to an above-described genetically modified organism which contains two or more nucleic acids encoding a 8-7-isomerase and/or two or more nucleic acids encoding a 5-desaturase and/or two or more nucleic acids encoding a 24-reductase.

(485) In a preferred embodiment, the genetically modified organism has, compared to the wild type, in addition to the above-described genetic modifications a reduced activity of at least one of the activities selected from the group consisting of C24-methyltransferase activity and 22-desaturase activity.

(486) The reduction of at least one of the activities is preferably caused by reducing, compared to the wild type, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding a C24-methyltransferase and nucleic acids encoding a 22-desaturase.

(487) A particularly preferred genetically modified organism has, apart from the above-described genetic modifications, no functional C24-methyltransferase gene and/or 22-desaturase gene.

(488) Particular preference is given to above-mentioned genetically modified organisms in which the genetic modification additionally increases at least one of the activities selected from the group consisting of HMG-CoA-reductase activity, lanosterol-C14-demethylase activity, squalene-epoxidase activity, squalene-synthetase activity and sterol-acyltransferase activity compared to a wild type.

(489) Preferably, at least one of these activities is increased, as mentioned above, by increasing, compared to the wild type, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

(490) Preferably, gene expression of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase is increased compared to the wild type by increasing in the organism the copy number of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

(491) Accordingly, the invention preferably relates to an above-described genetically modified organism which contains two or more of at least one nucleic acid selected from the group consisting of nucleic acids encoding an HMG-CoA-reductase activity, nucleic acids encoding a lanosterol-C14-demethylase, nucleic acids encoding a squalene epoxidase, nucleic acids encoding a squalene synthetase and nucleic acids encoding a sterol acyltransferase.

(492) In particular, the invention preferably relates to a genetically modified organism which contains, in addition to the above-described genetic modifications, two or more nucleic acids encoding an HMG-CoA-reductase and/or two or more nucleic acids encoding a lanosterol-C14-demethylase and/or two or more nucleic acids encoding a squalene epoxidase and/or two or more nucleic acids encoding a squalene synthetase and/or two or more nucleic acids encoding a sterol acyltransferase.

(493) The above-described genetically modified organisms have, compared to the wild type, an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof.

(494) Accordingly, the invention relates to an above-described genetically modified organism which, compared to the wild type, has an increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof.

(495) Preferred genetically modified organisms are yeasts or fungi which have been genetically modified according to the invention, in particular yeasts which have been genetically modified according to the invention, in particular the yeast species Saccharomyces cerevisiae which has been genetically modified according to the invention, in particular the genetically modified yeast strains Saccharomyces cerevisiae AH22, Saccharomyces cerevisiae GRF, Saccharomyces cerevisiae DBY747 and Saccharomyces cerevisiae BY4741.

(496) In the scope of the present invention, increasing the content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof preferably means the artificially acquired ability to produce biosynthetically an increased amount of at least one of these compounds mentioned above in the genetically modified organism compared to the genetically unmodified organism.

(497) Accordingly, as mentioned at the beginning, wild type preferably means the genetically unmodified organism, but in particular the reference organism mentioned above.

(498) An increased content of 7-dehydrocholesterol and/or of the biosynthetic intermediates and/or secondary products thereof in comparison with the wild type means in particular the increase in the content of at least one of the abovementioned compounds in the organism by at least 50%, preferably 100%, more preferably 200%, particularly preferably 400%, in comparison with the wild type.

(499) The content of at least one of the mentioned compounds is preferably determined according to analytical methods known per se and preferably refers to those compartments of the organism, in which sterols are produced.

(500) The invention is illustrated by the following examples but is not limited to them:

I. GENERAL EXPERIMENTAL CONDITIONS

(501) 1. Restriction

(502) Restriction of the plasmids (1 to 10 g) was carried out in 30 l reaction mixtures. For this purpose, the DNA was taken up in 24 l of H.sub.2O and admixed with 3 l of the appropriate buffer, 1 ml of BSA (bovine serum albumin) and 2 l of enzyme. The enzyme concentration was 1 unit/l or 5 units/l, depending on the amount of DNA. In some cases, 1 l of RNase was added to the reaction mixture in order to degrade the tRNA. The restriction mixture was incubated at 37.degree. C. for 2 hours. The restriction was monitored using a minigel.

(503) 2. Gel Electrophoreses

(504) The gel electrophoreses were carried out in minigel or wide minigel apparatuses. The minigels (approx. 20 ml, 8 pockets) and the wide minigels (50 ml, 15 or 30 pockets) consisted of 1% strength agarose in TAE. The running buffer used was 1.times.TAE.

(505) After adding 3 l of stop solution, the samples (10 l) were applied. A-DNA cut with HindIII (bands at: 23.1 kb; 9.4 kb; 6.6 kb; 4.4 kb; 2.3 kb; 2.0 kb; 0.6 kb) served as standard. For fractionation, a voltage of 80 V was applied for 45 to 60 min. Thereafter, the gel was stained in ethidium bromide solution and documented under UV light using the INTAS video documentation system or photographed using an orange filter.

(506) 3. Gel Elution

(507) The desired fragments were isolated by means of gel elution. The restriction mixture was applied to several pockets of a minigel and fractionated. Only -HindIII and a sacrifice lane were stained in ethidium bromide solution, examined under UV light, and the desired fragment was marked. This prevented the DNA of the remaining pockets from being damaged by ethidium bromide and UV light. Putting the stained and unstained gel slices side by side made it possible to excise the desired fragment from the unstained gel slice on the basis of the marking. The agarose slice with the fragment to be isolated was introduced into a dialysis tube, sealed in air-bubble-free together with a small amount of TAE buffer and introduced into the BioRad minigel apparatus. The running buffer was 1.times.TAE and the voltage was 100 V for 40 min. Afterward, the polarity was switched for 2 min in order to redissolve DNA sticking to the dialysis tube. The buffer in the dialysis tube, which contained the DNA fragments, was transferred to reaction vessels and subjected to ethanol precipitation. For this purpose, 1/10 volume of 3M sodium acetate, tRNA (1 l per 50 l of solution) and 2.5 volumes of ice-cold 96% strength ethanol were added to the DNA solution. The mixture was incubated at 20.degree. C. for 30 min and then removed by centrifugation at 12 000 rpm, 4.degree. C., 30 min. The DNA pellet was dried and taken up in 10 to 50 l of H.sub.2O (depending on the amount of DNA).

(508) 4. Klenow Treatment

(509) The Klenow treatment fills in protruding ends of DNA fragments, resulting in blunt ends. Per 1 g of DNA, the following reaction mixture was pipetted: DNA.times. .times. pellet+.times. 11.times. .times. .times. 1.times. .times. H 2.times. 0+.times. 1.5.times. .times. 10.times. Klenow.times. .times. buffer+.times. 1.times. .times. .times. I.times. .times. 0.1.times. .times. M.times. .times. DTT+.times. 1.times. .times. .times. I.times. .times. nucleotide.times. .times. (dNTP.times. .times. 2.times. .times. mM)+.times. 1.times. .times. .times. I.times. .times. Klenow.times. .times. polymerase.times. .times. (1.times. .times. unit/.times. .times. I) 25

(510) The DNA should be from an ethanol precipitation, in order to prevent contaminations from inhibiting the Klenow polymerase. The reaction mixture was incubated at 37.degree. C. for 30 min, and the reaction was stopped by incubating for another 5 min at 70.degree. C. The DNA was recovered from the reaction mixture by ethanol precipitation and taken up in 10 l of H.sub.2O.

(511) 5. Ligation

(512) The DNA fragments to be ligated were combined. The final volume of 13.1 l contained approx. 0.5 l of DNA with a vector/insert ratio of 1:5. The sample was incubated at 70.degree. C. for 45 seconds, cooled to room temperature (approx. 3 min) and then incubated on ice for 10 min. The ligation buffers were then added: 2.6 l of 500 mM Tris-HCl pH 7.5 and 1.3 l of 100 mM MgCl.sub.2, followed by incubation on ice for a further 10 min. After adding 1 l of 500 mM DTT and 1 l of 10 mM ATP and another 10 min on ice, 1 l of ligase (1 unit/pl) was added. The whole treatment should be carried out as free from vibrations as possible so that adjoining DNA ends are not separated again. The ligation was carried out at 14.degree. C. over night.

(513) 6. Transformation of E. Coli

(514) Competent Escherichia coli (E. coli) NM522 cells were transformed with the DNA of the ligation mixture. A reaction mixture containing 50 g of the pScL3 plasmids and a reaction mixture without DNA were run as positive control and zero control, respectively. For each transformation mixture, 100 l of 8% PEG solution, 10 l of DNA and 200 l of competent cells (E. coli NM522) were pipetted into a benchtop-centrifuge tube. The reaction mixtures were put on ice for 30 min and agitated occasionally.

(515) Then the heat shock was carried out: 1 min at 42.degree. C. For regeneration, 1 ml of LB medium was added to the cells and the suspension was incubated on a shaker at 37.degree. C. for 90 min. In each case, 100 l of the undiluted reaction mixtures, a 1:10 dilution and a 1:100 dilution were plated on LB+ampicillin plates and incubated at 37.degree. C. over night.

(516) 7. Plasmid Isolation from E. Coli (Miniprep)

(517) E. coli colonies were grown in 1.5 ml of LB+ampicillin medium in benchtop-centrifuge tubes at 37.degree. C. and 120 rpm over night. On the next day, the cells were removed by centrifugation at 5000 rpm and 4.degree. C. for 5 min and the pellet was taken up in 50 l of TE buffer. 100 l of 0.2 N NaOH, 1% SDS solution were added to and mixed with each reaction mixture, and the mixture was put on ice for 5 min (lysis of the cells). Then, 400 l of Na acetate/NaCl solution (230 l of H.sub.2O, 130 l of 3 M sodium acetate, 40 l of 5M NaCl) were added, the reaction mixture was mixed and put on ice for a further 15 min (protein precipitation). After centrifugation at 11 000 rpm for 15 minutes, the supernatant containing the plasmid DNA was transferred to an Eppendorf vessel. If the supernatant was not completely clear, centrifugation was repeated. 360 l of ice-cold isopropanol were added to the supernatant and the reaction mixture was incubated at 20.degree. C. for 30 min (DNA precipitation). The DNA was removed by centrifugation (15 min, 12 000 rpm, 4.degree. C.), the supernatant was discarded, the pellet was washed in 100 l of ice-cold 96% strength ethanol, incubated at 20.degree. C. for 15 min and again removed by centrifugation (15 min, 12 000 rpm, 4.degree. C.). The pellet was dried in a Speed Vac and then taken up in 100 l of H.sub.2O. The plasmid DNA was characterized by restriction analysis. For this purpose, 10 l of each reaction mixture were restriction-digested and fractionated gel-electrophoretically in a wide minigel (see above).

(518) 8. Plasmid Preparation from E. Coli (Maxiprep)

(519) In order to isolate larger amounts of plasmid DNA, the maxiprep method was carried out. Two flasks with 100 ml of LB+ampicillin medium were inoculated with a colony or with 100 l of a frozen culture which carries the plasmid to be isolated and incubated at 37.degree. C. and 120 rpm over night. On the next day, the culture (200 ml) was transferred to a GSA beaker and centrifuged at 4000 rpm (2600.times.g) for 10 min. The cell pellet was taken up in 6 ml of TE buffer. The cell wall was digested by adding 1.2 ml of lysozyme solution (20 mg/ml of TE buffer) and incubated at room temperature for 10 min. Subsequently, the cells were lysed with 12 ml of a 0.2 N NaOH, 1% SDS solution, followed by incubation at room temperature for another 5 min. The proteins were precipitated by adding 9 ml of a cooled 3 M sodium acetate solution (pH 4.8) and incubation on ice for 15 minutes. After centrifugation (GSA: 13 000 rpm (27 500.times.g), 20 min, 4.degree. C.), the supernatant containing the DNA was transferred to a new GSA beaker and the DNA was precipitated with 15 ml of ice-cold isopropanol and incubation at 20.degree. C. for 30 min. The DNA pellet was washed in 5 ml of ice-cold ethanol and dried in air (approx. 30-60 min). Thereafter, it was taken up in 1 ml of H.sub.2O. The plasmid was checked by restriction analysis. The concentration was determined by applying dilutions to a minigel. The salt content was reduced by microdialysis (pore size 0.025 m) for 30-60 minutes.

(520) 9. Transformation of Yeast

(521) For the transformation of yeast, a preculture of the strain Saccharomyces cerevisiae AH22 was prepared. A flask containing 20 ml of YE medium was inoculated with 100 l of the frozen culture and incubated at 28.degree. C. and 120 rpm over night. The main culture was carried out under the same conditions in flasks containing 100 ml of YE medium which was inoculated with 10 l, 20 l or 50 l of the preculture.

(522) 9.1 Preparation of Competent Cells

(523) On the next day, the cells in the flasks were counted by means of a Thoma chamber and the flask containing from 3-5.times.10.sup.7 cells/ml was chosen for the subsequent procedure. The cells were harvested by centrifugation (GSA: 5000 rpm (4000.times.g) 10 min). The cell pellet was taken up in 10 ml of TE buffer and distributed into two benchtop-centrifuged tubes (5 ml each). The cells were removed by centrifugation at 6000 rpm for 3 min and then washed twice with in each case 5 ml of TE buffer. The cell pellet was then taken up in 330 l of lithium acetate buffer per 10.sup.9 cells, transferred to a sterile 50 ml Erlenmeyer flask and agitated at 28.degree. C. for one hour. As a result, the cells were competent for transformation.

(524) 9.2 Transformation

(525) For each transformation mixture, 15 l of herring sperm DNA (10 mg/ml), 10 l of the DNA to be transformed (approx. 0.5 g) and 330 l of competent cells were pipetted into a benchtop-centrifuged tube and incubated at 28.degree. C. for 30 min (without agitation). Then, 700 l of 50% PEG 6000 were added and the suspension was incubated at 28.degree. C. for another hour, without agitation. This was followed by a heat shock at 42.degree. C. for 5 min. 100 l of the suspension were plated on selection medium (YNB, Difco) in order to select for leucine prototrophy. In the case of selection for G418 resistance, the cells are regenerated after the heat shock (see under 9.3 Regeneration phase).

(526) 9.3 Regeneration Phase

(527) Since the selection marker is the resistance to G418, the cells needed time to express the resistance gene. 4 ml of YE medium were added to the transformation mixtures which were then incubated on the shaker (120 rpm) at 28.degree. C. over night. On the next day, the cells were removed by centrifugation (6000 rpm, 3 min), taken up in 1 ml YE medium, and 100 l or 200 l thereof were plated on YE+G418 lates. The plates were incubated at 28.degree. C. for several days.

(528) 10. PCR Reaction Conditions

(529) The reaction conditions for the polymerase chain reaction must be optimized in each individual case and do not apply absolutely to each reaction mixture. Thus it is possible, inter alia, to vary the amount of DNA used, the salt concentrations and the melting temperature. For our task, it proved advantageous to combine in an Eppendorf vessel which was suitable for use in a thermocycler the following substances: 5 l of Super buffer, 811 of dNTPs (0.625 M each), 5 primer, 3 primer and 0.2 g of template DNA, dissolved in enough water so as to result in a total volume of 50 l for the PCR reaction mixture, were added to 2 l of (=0.1 U) Super Taq polymerase. The reaction mixture was briefly centrifuged and overlaid with a drop of oil. Between 37 and 40 cycles were chosen for amplification.

II. EXAMPLES

Example 1

(530) Expression and overexpression of a truncated HMG-CoA reductase, a squalene epoxidase (ERG1) and/or a lanosterol-C14-demethylase (ERG11), partially with deletion of ERG5 and ERG6 in S. cerevisiae GRF18 and GRFura3, respectively.

(531) 1.1 Preparation of the Plasmids pFlat1 and pFlat3 and pFlat4

(532) The expression vector pFlat3 was prepared by linearizing the plasmid YEp24 (Naumovski L, Friedberg E C (1982) Molecular cloning of eucaryotic genes required for excision repair of UV-irradiated DNA: isolation and partial characterization of the RAD.sub.3 gene of Saccharomyces cerevisiae. J Bacteriol October; 152(1):323-31) via restriction with Sphl and a 900 bp Sphl fragment of the vector pPT2B (Lang C, Looman A C. (1995) Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae. Appl Microbiol Biotechnol. December; 44(1-2): 147-56) which contains the ADH1 promoter and the TRP1 terminator of the yeast Saccharomyces cerevisiae and a multiple-cloning site of the vector pUC19 (Yanisch-Perron C, Vieira J, Messing J. (1985) Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13 mp18 and pUC19 vectors. Gene. 1985; 33(1): 103-19.) was integrated.

(533) The multiple-cloning site was extended by a polylinker containing the restriction sites NotI and Xhol. The polylinker was integrated via the Sall cleavage site of the vector. The resulting plasmid is denoted pFlat1.

(534) The vector pFlat3 was prepared by linearizing the vector pFlat1 by the enzyme Ncol and blunt-ending it by means of Klenow treatment. This was followed by integrating a BamHI fragment which had been blunt-ended by means of Klenow-polymerase treatment and which contains the yeast LEU2 gene and originates from the plasmid YDpL (Berben, G., Dumont, J., Gilliquet, V., Bolle, P. A. and Hilger F. (1991) The YDp Plasm ids: a Uniform Set of Vectors Bearing Versatile Disruption Cassettes for Saccharomyces cerevisiae. Yeast 7: 475-477.).

(535) The vector pFlat4 was prepared by linearizing the vector pFlat1 by the enzyme Ncol and blunt-ending it by means of Klenow treatment. This was followed by integrating a BamHI fragment which had been blunt-ended by means of Klenow-polymerase treatment and which contains the yeast HIS3 gene and originates from plasmid YDpH (Berben et al., 1991).

(536) 1.2 Integration of ERG1, ERG11, ERG4, ERG2 or ERG3 or of the 24-Reductase Gene into the Vectors pFLat1, pFlat3 and pFlat4

(537) First, a NotI restriction cleavage site was inserted at the 5-coding side of the genes ERG1, ERG11, ERG4, 24-reductase, ERG2 or ERG3 and an Xhol restriction cleavage site was inserted at the 3-coding side of said genes by means of PCR and the corresponding coding regions were amplified. Subsequently, the amplicons were treated with the restriction enzymes NotI and Xhol. The plasmids pFlat1, pFlat3 and pFlat4 were treated in parallel with enzymes NotI and Xhol. The cleaved amplicons were then integrated into the cleaved plasmids via ligation using T4 ligase. FIG. 7 depicts as an example the plasmid pFLAT-3-ERG4.

(538) Primer sequences for cloning ERG1, ERG11, ERG2, ERG3, ERG4, 24-reductase: TABLE-US-00002 Primer ERG1-5 (SEQ. ID. No. 51): CTGCGGCCGC ATCATGTCTG CTGTTAACGT TGC Primer ERG1-3 (SEQ. ID. No. 52): TTCTCGAGTT AACCAATCAA CTCACCAAAC Primer ERG11-5 (SEQ. ID. No. 53): CTGCGGCCGCAGGATGTCTGCTACCAAGTCAATCG Primer ERG11-3 (SEQ. ID. No. 54):

(539) ATCTCGAGCTTAGATCTTTTGTTCTGGATTTCTC Primer ERG2-5 (SEQ. ID. No. 55): CTGCGGCCGCACCATGAAGTTTTTCCCACT CC Primer ERG2-3 (SEQ. ID. No. 56): TTCTCGAGTTAGAACTTTTTGTTTTGCAACAAG Primer ERG3-5 (SEQ. ID. No. 57): CTGCGGCCGCAATATGGATTTGGTCTTAGAAGTCG Primer ERG3-3 (SEQ. ID. No. 58): AACTCGAGTCAGTTGTTCTTCTTGGTATTTG Primer ERG4-5 (SEQ. ID. No. 59): CTGCGGCCGCACTATGGCAAAGGATAATAGTGAG Primer ERG4-3 (SEQ. ID. No. 60): TTCTCGAGCTAGAAAACATAAGGAATAAAGAC Primer 24R-5 (SEQ. ID. No. 47): CTGCGGCCGCAAGATGGAGCCCGCCGTGTCGC Primer 24R-3 (SEQ. ID. No. 48) AACTCGAGTCAGTGCCTTGCCGCCTTGC 1.3 Preparation of the Integration Vectors pUG6-tHMG, pUG6-ERG1, pUG6-ERG11 1.3.1 pUG6-tHMG

(540) The DNA sequence for the expression cassette composed of ADH1-promoter-tHMG-tryptophan-terminator was isolated from the vector YepH2 (Polakowski, T., Stahl, U., Lang, C. (1998): Overexpression of a cytosolic HMG-CoA reductase in yeast leads to squalene accumulation. Appl. Microbiol. Biotechnol. 49: 66-71) by restriction with the enzymes EcoRV and Bsp68I (NruI) by using standard methods. The DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-tHMG (FIG. 1).

(541) 1.3.2 pUG6-ERG1

(542) The DNA sequence for the expression cassette composed of ADH1-promoter-ERG1-tryptophan-terminator was isolated from the vector pFlat3-ERG1 by restriction with the enzymes NheI and Bsp68I (NruI), using standard methods. After Klenow treatment, the DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-ERG1 (FIG. 2).

(543) 1.3.3 pUG6-ERG11

(544) The DNA sequence for the expression cassette composed of ADH1-promotor-ERG11-tryptophan-terminator was isolated from the vector pFlat3-ERG11 by restriction with the enzymes EcoRV and Bsp68I (NruI) using standard methods. The DNA fragment obtained was cloned with blunt ends into the EcoRV cleavage site of the vector pUG6 (Guldener, U et al. (1996): A new efficient gene disruption cassette for repeated use in budding yeast, Nucleic Acids Res. July 1; 24(13):2519-24), resulting in the vector denoted pUG6-ERG11 (FIG. 3).

(545) 1.4. Integrative Transformation of the Expression Cassettes into the Yeast Strains GRF or GRFura3

(546) After plasmid isolation, fragments of the vectors pUG6-tHMG, pUG6-ERG1 and pUG6-ERG11 were amplified by means of PCR in such a way that the resulting fragments consist of the following components: IoxP-kanMX-IoxP-ADH1 promoter-target gene-tryptophan terminator, with target gene meaning tHMG, ERG1 and, ERG11 and kanMX respectively, meaning a kanamycin-resistance gene.

(547) The selected primers were oligonucleotide sequences which contain in the annealing region the sequences beyond the cassettes to be amplified of the vector pUG6-target gene and which contain at the 5 and 3 protruding ends in each case 40 base pairs of the 5 or 3 sequence of the integration locus. This ensures that on the one hand the entire fragment, including KanMX and target gene, is amplified and, on the other hand, this fragment can then be transformed into yeast and be integrated by homologous recombination into the target gene locus of the yeast. Depending on the target gene locus in the yeast, the following oligonucleotide sequences were used as primers:

(548) For integration at the URA3 gene locus: TABLE-US-00003 For integration at the URA3 gene locus: URA3-Crelox-5 (SEQ. ID. No. 33): 5-ATGTCGAAAG CTACATATAA GGAACGTGCT GCATCTCATC CCAGCTGAAG CTTCGTACGC-3 URA3-Crelox-3 (SEQ. ID. No. 34): 5-TTAGTTTTGC TGGCCGCATC TTCTCAAATA TGCTTCCCAG GCATAGGCCA CTAGTGGATC TG-3 For integration at the LEU2 gene locus: LEU2-Crelox-5 (SEQ. ID. No. 35): 5-GAATACTCAG GTATCGTAAG ATGCAAGAGT TCGAATCTCT CCAGCTGAAG CTTCGTACGC-3 LEU2-Crelox-3 (SEQ. ID. No. 36): 5-TCTACCCTAT GAACATATTC CATTTTGTAA TTTCGTGTCG GCATAGGCCA CTAGTGGATC TG-3

(549) For integration at the HIS3 gene locus: TABLE-US-00004 HIS3-Crelox-5 (SEQ. ID. No. 37): 5-ATGACAGAGC AGAAACCCCT AGTAAAGCGT ATTACAAATG CCAGCTGAAG CTTCGTACGC-3 HIS3-Crelox-3 (SEQ. ID. No. 38): 5-CTACATAAGA ACACCTTTGG TGGAGGGAAC ATCGTTGGTA GCATAGGCCA CTAGTGGATC TG-3

(550) For integration at the ERG6 gene locus: TABLE-US-00005 ERG6-Crelox-5 (SEQ. ID. No. 39): 5-ATGAGTGAAA CAGAATTGAG AAAAAGACAG GCCCAATTCA CCAGCTGAAG CTTCGTACGC-3 ERG6-Crelox-3 (SEQ. ID. No. 40): 5-TTATTGAGTT GCTTCTTGGG AAGTTTGGGA GGGGGTTTCG GCATAGGCCA CTAGTGGATC TG-3

(551) For integration at the ERG5 gene locus: TABLE-US-00006 ERG5-Crelox-5 (SEQ. ID. No. 41): 5-ATGAGTTCTG TCGCAGAAAA TATAATACAA CATGCCACTC CCAGCTGAAG CTTCGTACGC-3 ERG5-Crelox-3 (SEQ. ID. No. 42): 5-TTATTCGAAG ACTTCTCCAG TAATTGGGTC TCTCTTTTTG GCATAGGCCA CTAGTGGATC TG-3

(552) The resistance to Geneticin (G418) served as selection marker. The resulting strains contained a copy of the particular target gene (tHMG, ERG1 or ERG11) under the control of the ADH promoter and the tryptophan terminator. At the same time, it was possible to delete the particular gene of the target locus by integrating the expression cassette. In order to subsequently remove again the gene for G418 resistance, the resultant yeast strain was transformed with the cre recombinase-containing vector pSH47 (Guldener U, Heck S, Fielder T, Beinhauer J, Hegemann J H. (1996) A new efficient gene disruption cassette for repeated use in budding yeast. Nucleic Acids Res. July 1; 24(13):2519-24). This vector caused the expression of cre recombinase in the yeast, and, as a consequence, the sequence region within the two IoxP sequences was removed by recombination, and this in turn resulted in only one of the two IoxP sequences and the ADH1 promoter-target gene-tryptophan terminator expression cassette remaining in the target gene locus.

(553) As a consequence, the yeast strain loses its G418 resistance again and is therefore suitable for integrating or removing further genes by means of this cre-lox system into or from said yeast strain. The vector pSH47 can then be removed selectively by cultivation on FOA medium.

(554) Thus it is possible to integrate a plurality of target genes successively into the yeast strain under the control of the ADH1 promoter and tryptophan terminator at various target loci.

(555) First, a target gene is integrated at the URA3 locus or a ura3 strain is used in order to render the yeast strain uracil-auxotrophic, since the vector pSH47 contains a URA3 gene for selection of uracil-prototrophic strains. FIG. 4 shows an example of the method.

(556) This method produced the yeast integration and deletion strains listed in Table 1, with, in a manner known per se, the gene in lower-case letters representing a deletion and the gene in capital letters representing an integration.

(557) TABLE-US-00001 TABLE 1 Modification No. Strain name No. Strain name compared to GRF yeast strain I GRFtH1 ura3, tHMG:leu2 II GRFth1e1 ERG1:ura3, tHMG:leu2 III GRFtH1E11 ura3, tHMG:leu2, ERG11:his3 IV GRFtH1E1E11 ERG1:ura3, tHMG:leu2, ERG11:his3 V GRFtH1E1E11erg5erg6 ura3, tHMG:leu2, ERG1:erg6, ERG11:erg5 VI GRFtH1erg5erg6 ura3, tHMG:leu2, erg5, erg6

(558) The yeast strains were cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(559) After 3 days, the sterols and squalene were extracted (Parks L W, Bottema C D, Rodriguez R J, Lewis T A. (1985) Yeast sterols: yeast mutants as tools for the study of sterol metabolism. Methods Enzymol. 1985; 111:333-46.) and analyzed by means of gas chromatography. The following values were obtained (see Table 2).

(560) TABLE-US-00002 Content of sterols 1 to 11 in [peak area/gTS] No. Strain name 1 2 3 4 5 6 7 8 9 10 11 I GRFtH1 9.9 0.8 0.3 1.2 1.1 1.0 0.0 0.0 0.0 0.0 4.7 II GRFtH1E1 6.8 1.9 0.4 1.5 2.2 2.1 0.0 0.0 0.0 0.0 6.9 III GRFtH1E11 9.9 0.4 0.7 2.3 1.9 1.9 0.0 0.0 0.0 0.0 5.0 IV GRFtH1E1E11 6.0 1.2 0.9 3.0 2.3 2.2 0.0 0.0 0.0 0.0 7.2 V GRFtH1E1E11 5.8 0.8 0.4 23.1 0.0 0.0 0.0 0.0 11.8 0.0 0.0 erg5erg6 VI GRFtH1erg5erg6 9.9 0.8 0.3 12.6 0.0 0.0 0.0 0.0 7.1 0.0 0.0 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 2

(561) Expression of the Heterologous Gene Encoding a 8-7-Isomerase (Ebp) from Mice (Mus musculus) in Yeast

(562) The cDNA sequence of Mus musculus 8-7-isomerase (Moebius, F. F., Soellner, K. E. M., Fiechter, B., Huck, C. W., Bonn, G., Glossmann, H. (1999): Histidine77, Glutamic Acid123, Threonine126, Asparagine194, and Tryptophan197 of Human Emopamil Protein Are Required for in Vivo Sterol 8-7 Isomerisation. Biochem. 38, 1119-1127) was amplified by PCR from the cDNA clone IMAGp998A22757 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin).

(563) The primers used here are the DNA oligomers Ebp-5 (SEQ. ID. No. 43) and Ebp-3 (SEQ. ID. No. 44). The DNA fragment obtained was treated with restriction enzymes NotI and Xhol and then integrated into the vectors pFlat3 and pFlat1 (FIG. 4) which likewise been treated with the enzymes NotI and Xhol beforehand by means of a ligase reaction. The resulting vectors pFlat1-EBP and pFlat3-EBP (FIG. 5a) contain the EBP gene under the control of the ADH promoter and the tryptophan terminator.

(564) The expression vector pFlat3-EBP was then transformed into the yeast strains I to VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(565) The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus 8-7-isomerase in combination with the experssion of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 3. The abbreviations have the following meanings: =decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

(566) TABLE-US-00003 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 VII GRFtH1 0 0 0 0 0 0 / / / / 0 pFlat3-Ebp VIIII GRFtH1E1 0 0 0 0 0 + / / / 0 pFlat3-Ebp IX GRFtH1E11 pFlat3- 0 0 0 0 0 + / / / 0 Ebp X GRFtH1E1E11 pFlat3- 0 0 0 0 0 + / / / 0 Ebp XI GRFtH1E1E11erg5erg6 0 0 0 / / + / ++ / / pFlat3-Ebp XII GRFtH1erg5erg6 0 0 0 / / + / + / / pFlat3-Ebp 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 3

(567) Expression of the Heterologous Gene Encoding a 5-Desaturase (Sc5d) from Mice (Mus musculus) in Yeast

(568) The cDNA sequence of Mus musculus 5-desaturase (Nishi, S., Hideaki, N., Ishibashi, T. (2000): cDNA cloning of the mammalian sterol C5-desaturase and the expression in yeast mutant. Biochim. Biophys. A 1490, 106-108) was amplified by PCR from the cDNA clone IMAGp998K144618 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin). The primers used here are the DNA oligomers Sc5d-5 (SEQ. ID. No. 45) and Sc5d-3 (SEQ. ID. No. 46). The DNA fragment obtained was treated with restriction enzymes NotI and Xhol and then integrated into the vector pFlat3 (FIG. 4) which likewise had been treated with the enzymes NotI and Xhol beforehand, by means of a ligase reaction. The resulting vector pFlat3-SC5D (FIG. 5b) contains the SC5D gene under the control of the ADH promoter and the tryptophan terminator.

(569) The expression vector pFlat3-SC5D was then transformed into the yeast strains I to VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(570) The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus 5-desaturase in combination with the experssion of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 4. The abbreviations have the following meanings: =decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

(571) TABLE-US-00004 TABLE 4 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XIII GRFtH1 pFlat3-Sc5d 0 0 0 0 0 0 / / / / 0 XIV GRFtH1E1 pFlat3-Sc5d 0 0 0 0 0 / / + / 0 XV GRFtH1E11 0 0 0 0 0 / / + / 0 pFlat3-Sc5d XVI GRFtH1E1E11 0 0 0 0 0 / / + / 0 pFlat3-Sc5d XVII GRFtH1E1E11erg5erg6 0 0 / / / / +++ + / pFlat3-Sc5d XVIII GRFtH1erg5erg6 0 0 0 / / / / ++ / / pFlat3-Sc5d 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 4

(572) Expression of the Heterologous Gene Encoding a 24-Reductase (D24R) from Mice (Mus musculus) in Yeast

(573) The cDNA sequence of Mus musculus 24-reductase (Waterham, H. R., Koster, J., Romeijn, G. J., Hennekam, R. C., Vreken, P., Andersson, H. C., FitzPatrick, D. R., Kelley, R. I. and Wanders, R. J., Mutations in the 3-Hydroxysterol 24-Reductase Gene Cause Desmosterolosis, an Autosomal Recessive Disorder of Cholesterol Biosynthesis, Am. J. Hum. Genet. 69 (4), 685-694 (2001)) was amplified by PCR from the cDNA clone IMAGp998K179532 (Host: E. coli DH10B) of the Deutsches Resourcenzentrum fur Genomforschung [German resource center for genome research] GmbH (Berlin).

(574) The primers used here are the DNA oligomers D24R-5 (SEQ. ID. No. 47) and D24R-3 (SEQ. ID. No. 48). The DNA fragment obtained was treated with restriction enzymes NotI and Xhol and then integrated into the vector pFlat4 (FIG. 6) which likewise had been treated with the enzymes NotI and Xhol beforehand, by means of a ligase reaction. The resulting vector pFlat4-D24R (FIG. 5d) contains the D24R gene under the control of the ADH1 promoter and the tryptophan terminator.

(575) The expression vector pFlat4-D24R was then transformed into the yeast strains I to VI of Table 1 from Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(576) The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a Mus musculus 24-reductase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 5. The abbreviations have the following meanings: =decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

(577) TABLE-US-00005 TABLE 5 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XIX GRFtH1 0 0 0 0 0 0 / / / / 0 pFlat4-D24R XX GRFtH1E1 0 0 0 / / / + 0 pFlat4-D24R XXI GRFtH1E11 pFlat4- 0 0 0 0 0 / + / + 0 D24R XXII GRFtH1E1E11 pFlat4- 0 0 0 0 0 / + / + 0 D24R XXIII GRFtH1E1E11erg5erg6 0 / / 0 + + +++ / pFlat4-D24R XXIV GRFtH1erg5erg6 0 / / 0 + + ++ / pFlat4-D24R 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 5

(578) Coexpression of the Heterologous Genes Encoding a 8-7-Isomerase (Ebp) from Mice (Mus musculus) and a C5-Desaturase (Sc5d) from Mice (Mus musculus) in Yeast

(579) The expression vectors pFlat1-EBP (from Example 2) and pFlat3-SC5D (from Example 3) were transformed into the yeast strains I to VI of Table 1 of Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(580) The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a 8-7-isomerase and a Mus musculus C5-desaturase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 6. The abbreviations have the following meanings: =decrease; 0=no change; /=not present; +, ++, +++, ++++=concentrated to highly concentrated.

(581) TABLE-US-00006 TABLE 6 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 VVX GRFtH1 pFlat3-Ebp/ 0 0 0 0 0 / / + / 0 pFlat1-Sc5d XXVI GRFtH1E1 pFlat3-Ebp/ 0 0 0 0 / / + / 0 pFlat1-Sc5d XXVII GRFtH1E11 pFlat3- 0 0 0 0 0 / / + / 0 Ebp/pFlat1-Sc5d XXVIII GRFtH1E1E11 pFlat3- 0 0 0 / / ++ / 0 Ebp/pFlat1-Sc5d XXIX GRFtH1E1E11erg5erg6 0 0 / / / / +++ + / pFlat3-Ebp/pFlat1- Sc5d XXX GRFtH1erg5erg6 0 0 0 / / / / ++ + / pFlat3-Ebp/pFlat1- Sc5d 1 = Squalene 2 = Lanosterol 3 = Dimethylzymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol

Example 6

(582) Coexpression of the Heterologous Genes Encoding a 8-7-Isomerase (Ebp) from Mice (Mus musculus) Encoding a C5-Desaturase (Sc5d) from Mice (Mus musculus) and a 24-Reductase from Mice (Mus musculus) in Yeast

(583) The expression vectors pFlat1-EBP (from Example 2) and pFlat3-SC5D (from Example 3) and pFlat4-D24R (from Example 4) were transformed into the yeast strains I to VI of Table 1 of Example 1 and also into the GRFura3 strain. The yeast strains obtained in this way were then cultured in a culture volume of 20 ml in WMVIII medium at 28.degree. C. and 160 rpm for 48 hours. Subsequently, 500 l of this preculture were transferred to a 50 ml main culture of the same medium and cultured in a baffled flask at 28.degree. C. and 160 rpm for 3 days.

(584) The sterols were extracted after 3 days and analyzed by means of gas chromatography, as described in Example 1. The influence of the expression of a 8-7-isomerase, a Mus musculus C5-desaturase and a Mus musculus 24-reductase in combination with the expression of the transcriptionally deregulated intrinsic yeast genes tHMG and/or ERG1 and/or ERG11 and/or deletion of the intrinsic yeast genes ERG6 and ERG5 is listed in Table 7. The abbreviations have the following meanings: =decrease; 0=no change; /=not present; ++, +++, ++++=concentrated to highly concentrated.

(585) TABLE-US-00007 TABLE 7 Influence of the genetic modifications on the sterol content compared to the GRF yeast strain No. Strain name 1 2 3 4 5 6 7 8 9 10 11 XXXI GRFtH1 pFlat3-Ebp/ 0 0 0 0 0 / / / + 0 pFlat1-Sc5d/pFlat4- D24R XXXII GRFtH1E1 pFlat3-Ebp/ 0 0 0 0 / / / + 0 pFlat1-Sc5d/pFlat4- D24R XXXIII GRFtH1E11 pFlat3- 0 0 0 0 0 / / / + 0 Ebp/pFlat1-Sc5d/ pFlat4-D24R XXXIV GRFtH1E1E11 pFlat3- 0 0 0 / / / + 0 Ebp/pFlat1-Sc5d/ pFlat4-D24R XXXV GRFtH1E1E11erg5erg6 0 0 / / / / + ++++ / pFlat3-Ebp/pFlat1- Sc5d/pFlat4-D24R XXXVI GRFtH1erg5erg6 0 0 0 / / / / ++ +++ / pFlat3-Ebp/pFlat1- Sc5d/pFlat4-D24R 1 = Squalene 2 = Lanosterol 3 = Dimethyl zymosterol 4 = Zymosterol 5 = Fecosterol 6 = Episterol 7 = Cholesta-7,24-dienol 8 = Cholesta-8-enol 9 = Cholesta-5,7,24 trienol 10 = 7-Dehydrocholesterol 11 = Ergosterol