| dc.description | A DNA fragment originally detected in Streptomyces venezuelae ISP5230 DNA by hybridization with the actI gene for actinorhodin biosynthesis in Streptomyces coelicolor A3(2), and cloned from the S. venezuelae genome as a 1.8-kb SacI-BglII fragment, was used to probe a Sau3A1 genomic library of S. venezuelae in a lambda vector. Three hybridizing lambda clones contained DNA inserts with overlapping regions. Regions hybridizing with both actI and actIII (a second gene for actinorhodin biosynthesis) were located in the genomic DNA, and were adjacent. Subcloning and sequencing of a 4.9-kb segment of the insert containing these regions identified five open reading frames (ORFs). The deduced products of the ORFs closely resembled in sequence the components of streptomycete type II polyketide synthases (PKSs). From sequence comparisons it was concluded that the ORF1 product encodes a ketoacyl synthase, ORF2 a closely related product probably involved in determining chain length; ORF3 an acyl carrier protein, ORF4 a bifunctional cyclase/dehydrase, and ORF5 a ketoreductase. Integration into the S. venezuelae chromosome of pJV63, containing an insert from the ORF2-ORF4 region, severely depressed jadomycin B biosynthesis. Since the two integrants showed no change in growth or spore pigmentation, the cloned PKS genes are presumed to encode enzymes in the pathway for jadomycin B biosynthesis. | en_US |
