Identification of genes coding enzymes for ascomycin tetra-hydropyranose ring formation

Macrocyclic polyketides have generated great interest in biosynthetic chemistry because of the structural complexity and medicinal activities. The synthetic genes consist of the number and type of active sites of modular polyketide synthases. The cosmid library - prepared with the ascomycin (an antibiotics with immunosuppressive activity) - producer, Streptomyces sp. AA6554 genome was screened with an ascomycin ketosynthase gene probe, and one and a half modules were isolated. Database analysis shows that one of the modules consists of the genes coding a series of enzymes for the tetra-hydropyranose ring synthesis.