Cloning of midecamycin biosynthetic genes from Streptomyces mycarofaciens 1748.

A genomic library from the midecamycin producing strain Streptomyces mycarofaciens 1748 was constructed in the Escherichia coli-Streptomyces shuttle cosmid vector pNJ1. Several clones were obtained with DNA homologous to polyketide synthase genes by using the Streptomyces coelicolor actI and actIII genes as hybridization probes. Restriction analysis of the plasmids pCN8B12, pCN6C5 and pCN11E11 showed that their molecular weights were 36, 48.5 and 41.6 kilobase, respectively, and that they contained overlapping regions of DNA. The regions homologous to the actI and actIII genes were localized by DNA hybridization. Transformation of the cloned DNA into the S. mycarofaciens blocked mutant 68 and into Streptomyces lividans TK24 resulted in the production of midecamycin-like substances by TLC and HPLC analyses.