Characterization and targeted disruption of a glycosyltransferase gene in the tylosin producer, Streptomyces fradiae.

An open reading frame, designated tylN, has been identified by sequence analysis at one end of the tylosin biosynthetic gene cluster of Streptomyces fradiae, alongside a cluster of genes encoding the biosynthesis of dTDP-deoxyallose. This 6-deoxyhexose sugar is converted to mycinose, via bis O-methylation, following attachment to the polyketide lactone during tylosin biosynthesis. The deduced product of tylN is similar to several glycosyltransferases, authentic and putative, and displays a consensus sequence motif that appears to be characteristic of a sub-group of such enzymes. Specific disruption of tylN within the S. fradiae genome resulted in the production of demycinosyl-tylosin, whereas other glycosyltransferase activities involved in tylosin biosynthesis were not affected. Evidently, tylN encodes deoxyallosyl transferase.