ACCUMULATION OF THE ANGUCYCLINE ANTIBIOTIC RABELOMYCIN AFTER DISRUPTION OF AN OXYGENASE GENE IN THE JADOMYCIN-B BIOSYNTHETIC GENE-CLUSTER OF STREPTOMYCES-VENEZUELAE

DNA from a region downstream of and overlapping the polyketide synthas e (PKS) gene cluster for jadomycin B biosynthesis in Streptomyces vene zuelae was cloned and sequenced. Analysis of the nucleotide sequence l ocated one complete ORF (ORF6), an incomplete one representing the 3' region of ORF4 in the PKS cluster, and a second incomplete one (ORF7). The deduced amino acid sequences for ORFs 6 and 7 resemble those of o xygenases. Since a plausible biosynthetic pathway for jadomycin B incl udes an angular polyketide intermediate that undergoes oxidative ring fission before condensation with an amino acid, we subcloned one of th e presumptive oxygenase genes (ORF6) in a segregationally unstable shu ttle vector (pHJL400) and disrupted it by inserting the gene for apram ycin resistance. Transformation of S. venezuelae with the disruption v ector and selection for apramycin resistance gave mutants blocked in j adomycin biosynthesis. Southern hybridization confirmed that gene repl acement had occurred. Cultures of the mutants accumulated a metabolite identified by comparison with an authentic sample as rabelomycin, a n on-nitrogenous polyketide-derived antibiotic originally isolated from Streptomyces olivaceus.