The purpose of the present invention is to provide a protein, said protein having an activity of synthesizing rhamnose from glucose, and a polynucleotide encoding the same. Provided are a rhamnose synthase derived from stevia and a method for producing rhamnose from glucose using a gene. Also provided is a method for producing a steviol glycoside using the rhamnose synthase derived from stevia.

A highly safe and highly heat-resistant L-rhamnose isomerase usable in the food industry and the production thereof are disclosed. The L-rhamnose isomerase is derived from a microorganism belonging to the genus Enterobacter, has a subunit molecular mass of 47 kDa as measured by SDS-PAGE, and has the following substrate specificities (A) isomerase activity that recognizes and reacts with a CHO group at C1 and an OH group at C2 of an aldose to convert the CHO group at C1 into an OH group and the OH group at C2 into a CO group, or recognizes and reacts with an OH group at C1 and a CO group at C2 of a ketose to convert the OH group at C1 into a CHO group and the CO group at C2 into an OH group; and (B) reactivity with L-rhamnose, L-lyxose, L-mannose, D-allose, D-ribose, and L-talose.

The purpose of the present invention is to provide a protein, said protein having an activity of synthesizing rhamnose from glucose, and a polynucleotide encoding the same. Provided are a rhamnose synthase derived from stevia and a method for producing rhamnose from glucose using a gene. Also provided is a method for producing a steviol glycoside using the rhamnose synthase derived from stevia.

The present invention is directed towards genetic modification of native gene encoding for D-tagatose 3-epimerase and rhamnose isomerase to substantially increase the expression level of these enzymes and use of the enzymes in a process to produce rare monosaccharides such as psicose and allose. Also disclosed in the present invention is expression constructs comprising the modified genes and a host cells to express the same.