Function of glycosyltransferase genes involved in urdamycin A biosynthesis

Background: Urdamycin A, the principle product of Streptomyces fradiae Tu27 17, is an angucycline-type antibiotic. The polyketide-derived aglycone moie ty is glycosylated at two positions, but only limited information is availa ble about glycosyltransferases involved in urdamycin biosynthesis. Results: To determine the function of three glycosyltransferase genes in th e urdamycin biosynthetic gene cluster, we have carried out gene inactivatio n and expression experiments. Inactivation of urdGT1a resulted in the predo minant accumulation of urdamycin B. A mutant lacking urdGT1b and urdGT1c ma inly produced compound 100-2. When urdGT1c was expressed in the urdGT1b/urd GT1c double mutant, urdamycin G and urdamycin A were detected. The mutant l acking all three genes mainly accumulated aquayamycin and urdamycinone B. E xpression of urdGT1c in the triple mutant led to the formation of compound 100-1, whereas expression of urdGT1a resulted in the formation of compound 100-2. Co-expression of urdGT1b and urdGT1c resulted in the production of 1 2b-derhodinosyl-urdamycin A, and co-expression of urdGT1a, urdGT1c and urdG T1c resulted in the formation of urdamycin A. Conclusions: Analysis of glycosyltransferase genes of the urdamycin biosynt hetic gene cluster led to an unambiguous assignment of each glycosyltransfe rase to a certain biosynthetic saccharide attachment step.