Abstract: Cloning，sequence analysis of the UDP-glycosyltransferase gene from Siraitia grosvenorii and its expression in E. coli were conducted to further explore the relationship between SgUDPG1 expression and mogroside Ⅴ biosynthesis. The UDP-glycosyltransferase cDNA fragments amplified from Siraitia grosvenorii transcriptome by rapid amplification of cDNA ends（RACE）and RT-PCR，and then the cloned gene of SgUDPG1 was inserted into vector pEASY-E1. The recombinant plasmid pEASY-E1-SgUDPG1 was expressed in a prokaryotic expression system after it was transformed into  E. coli BL21（DE3）.The fusion protein was analyzed by SDS-PAGE，Western-blotting and mass spectrometry. The results showed that a full-length SgUDPG1 cDNA of 1 959 bp including open reading frame（ORF）of 1 365 bp was isolated. The predicted SgUDPG1 protein has 454 amino acids with an estimated molecular mass of 51.2 kD and an isoelectric point of 5.39. The SgUDPG1 contains 6 conserved domains predicted by InterProScan，including PSPG-box motif which is a unique consensus sequence of glycosyltransferases involved in plant secondary metabolism. DGE analysis showed that the expression of SgUDPG1 in 50 d and 70 d increased 5.16 and 13.12 times respectively than the 3 d. The results of SDS-PAGE，Western-blotting and mass spectrometry demonstrated that the recombinant plasmid pEASY- E1-His-SgUDPG1 could express a fusion protein whose molecule mass is 5.3 kD larger than the predicted molecule mass. Therefore，the SgUDPG1 of Siraitia grosvenorii was cloned and successfully expressed in E. coli. This study will provide a foundation for studying the function of this UDP-glycosyltransferase.

Key words: Siraitia grosvenorii, UDP-glycosyltransferase, rapid amplification of cDNA ends, prokaryotic expression, fusion protein