Doxorubicin Overproduction in Streptomyces peucetius: Cloning and Characterization of the dnrU Ketoreductase anddnrV Genes and the doxA Cytochrome P-450 Hydroxylase Gene

Doxorubicin-overproducing strains of Streptomyces peucetius ATCC 29050 can be obtained through manipulation of the genes in the region of the doxorubicin (DXR) gene cluster that containsdpsH, the dpsG polyketide synthase gene, the putative dnrU ketoreductase gene, dnrV, and thedoxA cytochrome P-450 gene. These five genes were characterized by sequence analysis, and the effects of replacingdnrU, dnrV, doxA, ordpsH with mutant alleles and of doxAoverexpression on the production of the principal anthracycline metabolites of S. peucetius were studied. The exact roles of dpsH and dnrV could not be established, although dnrV is implicated in the enzymatic reactions catalyzed by DoxA, but dnrU appears to encode a ketoreductase specific for the C-13 carbonyl of daunorubicin (DNR) and DXR or their biosynthetic precursors. The highest DXR titers were obtained in a dnrX dnrU (N. Lomovskaya, Y. Doi-Katayama, S. Filippini, C. Nastro, L. Fonstein, M. Gallo, A. L. Colombo, and C. R. Hutchinson, J. Bacteriol. 180:2379–2386, 1998) double mutant and a dnrX dnrU dnrH (C. Scotti and C. R. Hutchinson, J. Bacteriol. 178:7316–7321, 1996) triple mutant. Overexpression of doxA in adoxA::aphII mutant resulted in the accumulation of DXR precursors instead of in a notable increase in DXR production. In contrast, overexpression of dnrV and doxAjointly in the dnrX dnrU double mutant or the dnrX dnrU dnrH triple mutant increased the DXR titer 36 to 86%.