Hybridizing fragments in the genomic DNA of ISP5230, which produces the jadomycin group of angucycline antibiotics, were detected by probing with DNA from A3(2). The hybridizing regions were isolated from a 16.5 kb insert of λ replacement vector. Subcloning and sequencing of a 4.8 kb segment of the insert, containing regions hybridizing to as well as , identified five open reading frames (ORFs). The deduced polypeptide products of the ORFs closely resemble in sequence the components of streptomycete type-II polyketide synthases (PKSs): the ORF1 product corresponds to the ketoacyl synthase, and the ORF2 product to a polypeptide closely related to the ketoacyl synthase and involved in determining chain length; the ORF3 product matches the acyl carrier protein; ORF4 encodes a bifunctional cyclase/dehydrase; and ORF5 encodes a ketoreductase. Integration into the chromosomal DNA of a plasmid containing a segment of the ORF2-ORF4 region severely depressed jadomycin B biosynthesis; since the integrant showed no change in growth or spore pigmentation, the cloned PKS genes are presumed to encode enzymes in the pathway for jadomycin biosynthesis.


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