ISOLATION AND SEQUENCE-ANALYSIS OF POLYKETIDE SYNTHASE GENES FROM THEDAUNOMYCIN-PRODUCING STREPTOMYCES SP STRAIN C5

A contiguous region of about 30 kbp of DNA putatively encoding reactio ns in daunomycin biosynthesis was isolated from Streptomyces sp. strai n C5 DNA. The DNA sequence of an 8.1-kbp EcoRI fragment, which hybridi zed with actI polyketide synthase (PKS) and actIII polyketide reductas e (PKR) gene probes, was determined, revealing seven complete open rea ding frames (ORFs), two in one cluster and five in a divergently trans cribed cluster. The former two genes are Likely to encode PKR and a bi functional cyclase/dehydrase. The five latter genes encode: (i) a homo log of TcmH, an oxygenase of the tetracenomycin biosynthesis pathway; (ii) a PKS Orf1 homolog; (iii) a PKS Orf2 homolog (chain length factor ); (iv) a product having moderate sequence identity with Escherichia c oil beta-ketoacyl acyl carrier protein synthase m but lacking the cons erved active site; and (v) a protein highly similar to several acyltra nsferases. The DNA within the 8.1-kbp EcoRI fragment restored daunomyc in production to two dauA non-daunomycin-producing mutants of Streptom yces sp. strain C5 and restored wild-type antibiotic production to Str eptomyces coelicolor B40 (actVII; nonfunctional cyclase/dehydrase), an d to S. coelicolor B41 (actIII) and Streptomyces galilaeus ATCC 31671, strains defective in PKR activity.