Functional characterization of the jadI gene as a cyclase forming angucyclinones

A gene designated jadI from the jadomycin B producer Streptomyces venezuela e has homology to the tetracenomycin pathway tcmI gene and encodes a putati ve cyclase for angucyclinone biosynthesis. Expression in Streptomyces livid ans of a jadomycin (jad) gene cassette composed of the minimal polyketide s ynthase (PKS, jadABC), a cyclase (jadD), a ketoreductase (jadE), and jadI l eads to production of several yellow compounds in liquid culture. Rabelomyc in (1), a known angucyclinone, results from dehydration and oxidation of a new product, UWM6, isolated from the culture extracts. Characterization of UWM6 by UV, MS, and NMR analyses revealed a new angucyclinone structure, 4- hydroxy-12bH-12-deoxyrabelomycin. Production of these angucyclinones occurs only when jadI is present in the cassette, suggesting an essential cyclase phenotype for this gene. Engineered replacement of jadI in the jan cassett e with the tcmI cyclase gene, and similar replacement of tcmI in a function al tcm PKS cassette with jadI, leads to the same set of aromatic decapolyke tides produced by either cassette in the absence of jadI. From these result s we conclude that both cyclases are nonfunctional out of their normal cont ext.