CLONING AND CHARACTERIZATION OF POLYKETIDE SYNTHASE GENES FOR JADOMYCIN-B BIOSYNTHESIS IN STREPTOMYCES-VENEZUELAE ISP5230

Hybridizing fragments in the genomic DNA of Streptomyces venezuelae IS P5230, which produces the jadomycin group of angucycline antibiotics, were detected by probing with actl DNA from Streptomyces coelicolor A3 (2). The hybridizing regions were isolated from a 16.5 kb insert of S. venezuelae DNA recovered from a genomic library cloned in a ii replac ement vector. Subcloning and sequencing of a 4.8 kb segment of the ins ert, containing regions hybridizing to actIII as well as actl, identif ied five open reading frames (ORFs). The deduced polypeptide products of the ORFs closely resemble in sequence the components of streptomyce te type-ll polyketide synthases (PKSs): the ORF1 product corresponds t o the ketoacyl synthase, and the ORF2 product to a polypeptide closely related to the ketoacyl synthase and involved in determining chain le ngth; the ORF3 product matches the acyl carrier protein; ORF4 encodes a bifunctional cyclase/dehydrase; and ORF5 encodes a ketoreductase. In tegration into the chromosomal DNA of a plasmid containing a segment o f the ORF2-ORF4 region severely depressed jadomycin B biosynthesis; si nce the integrant showed no change in growth or spore pigmentation, th e cloned PKS genes are presumed to encode enzymes in the pathway for j adomycin biosynthesis.