REPEATED POLYKETIDE SYNTHASE MODULES INVOLVED IN THE BIOSYNTHESIS OF A HEPTAENE MACROLIDE BY STREPTOMYCES SP FR-008

Genes for biosynthesis of a Streptomyces sp. FR-008 heptaene macrolide antibiotic with antifungal and mosquito larvicidal activity were clon ed in Escherichia coli using heterologous DNA probes. The cloned genes were implicated in heptaene biosynthesis by gene replacement. The FR- 008 antibiotic contains a 38-membered, polyketide-derived macrolide ri ng. Southern hybridization using probes encoding domains of the type I modular erythromycin polyketide synthase (PKS) showed that the Strept omyces sp. FR-008 PKS gene cluster contains repeated sequences spannin g c. 105 kb of contiguous DNA; assuming c. 5 kb for each PKS module, t his is in striking agreement with the expectation for the 21-step cond ensation process required for synthesis of the FR-008 carbon chain. Th e methods developed for transformation and gene replacement in Strepto myces sp. FR-008 make it possible to genetically manipulate polyene ma crolide production, and may later lead to the biosynthesis of novel po lyene macrolides.