IDENTIFICATION OF STSC, THE GENE ENCODING THE L-GLUTAMINE-SCYLLO-INOSOSE AMINOTRANSFERASE FROM STREPTOMYCIN-PRODUCING STREPTOMYCETES

Eight new genes, strO-stsABCDEFG, were identified by sequencing DNA in the gene cluster that encodes proteins for streptomycin production of Streptomyces griseus N2-3-11. The StsA (calculated molecular mass 43. 5 kDa) and StsC (45.5 kDa) proteins - together with another gene produ ct, StrS (39.8 kDa), encoded in another operon of the same gene cluste r - show significant sequence identity and are members of a new class of pyridoxal-phosphate-dependent aminotransferases that have been obse rved mainly in the biosynthetic pathways for secondary metabolites, Th e aminotransferase activity was demonstrated for the first time by ide ntification of the overproduced and purified StsC protein as the L-glu tamine:scyllo-inosose aminotransferase, which catalyzes the first amin o transfer in the biosynthesis of the streptidine subunit of streptomy cin. The stsC and stsA genes each hybridized specifically to distinct fragments in the genomic DNA of most actinomycetes tested that produce diaminocyclitolaminoglycosides. In contrast. only stsC, but not stsA, hybridized to the DNA of Streptomyces hygroscopicus ssp. glebosus, wh ich produces the monoaminocyclitol antibiotic bluensomycin; this sugge sts that both genes are specifically used in the first and second step s of the cyclitol transamination reactions, Sequence comparison studie s performed with the deduced polypeptides of the genes adjacent to sts C suggest that the enzymes encoded by some of these genes [strO (putat ive phosphatase gene), stsB (putative oxidoreductase gene), and stsE ( putative phosphotransferase gene)] also could be involved in (di-)amin ocyclitol synthesis.