The present invention relates to an expression system for the heterologous expression of a nucleic acid sequence of interest in a mammalian cell, the system comprising: (i) a first genetic entity, comprising: a nucleic acid sequence encoding a functional Epstein Barr virus nuclear antigen 1 (EBNA-1), the nucleic acid sequence being operably linked to regulatory elements that allow for expression of the nucleic acid sequence encoding a functional EBNA-1; (ii) a second genetic entity, comprising: a nucleic acid sequence encoding a functional nucleoside diphosphate kinase A (NDPK-A), the nucleic acid sequence being operably linked to regulatory elements that allow for expression of the nucleic acid sequence encoding a functional NDPK-A; (iii) a third genetic entity, comprising: the nucleic acid sequence of interest being operably linked to regulatory elements that allow for expression of the nucleic acid sequence of interest; and (iv) a four genetic entity, comprising: the Epstein Barr virus OriP sequence or one or more subsequences thereof, wherein the one or more subsequences comprise at least the ‘Family of Repeats’ DNA-binding site for EBNA-1 and the ‘Dyad Symmetry’ DNA-binding site for EBNA-1. The present invention also relates to corresponding mammalian host cells and methods for expressing a nucleic acid sequence of interest by means of such expression system.

Provided herein, in some embodiments, are methods and composition for the production of nucleoside triphosphates and ribonucleic acids.

Provided herein, in some embodiments, are methods and composition for the production of nucleoside triphosphates and ribonucleic acids.

The present invention relates to an expression system for the heterologous expression of a nucleic acid sequence of interest in a mammalian cell, the system comprising: (i) a first genetic entity, comprising: a nucleic acid sequence encoding a functional Epstein Barr virus nuclear antigen 1 (EBNA-1), the nucleic acid sequence being operably linked to regulatory elements that allow for expression of the nucleic acid sequence encoding a functional EBNA-1; (ii) a second genetic entity, comprising: a nucleic acid sequence encoding a functional nucleoside diphosphate kinase A (NDPK-A), the nucleic acid sequence being operably linked to regulatory elements that allow for expression of the nucleic acid sequence encoding a functional NDPK-A; (iii) a third genetic entity, comprising: the nucleic acid sequence of interest being operably linked to regulatory elements that allow for expression of the nucleic acid sequence of interest; and (iv) a four genetic entity, comprising: the Epstein Barr virus OriP sequence or one or more subsequences thereof, wherein the one or more subsequences comprise at least the Family of Repeats DNA-binding site for EBNA-1 and the Dyad Symmetry DNA-binding site for EBNA-1. The present invention also relates to corresponding mammalian host cells and methods for expressing a nucleic acid sequence of interest by means of such expression system.

Provided herein, in some embodiments, are methods and composition for the production of nucleoside triphosphates and ribonucleic acids.