Expression of doxorubicin-daunorubicin resistance genes in different anthracycline-producing mutants of Streptomyces peucetius.
Two DNA fragments, ric1 and ric2, were isolated from the Streptomyces peucetius 7600 mutant, which produces daunorubicin and doxorubicin, on the basis of their abilities to confer doxorubicin and daunorubicin resistance to Streptomyces lividans. These two fragments are unrelated by restriction mapping and do not show any homology by Southern analysis, yet both of them increase the level of resistance 10-fold in transformed S. lividans. Functional analysis revealed that ric1 also contains two genes of daunorubicin biosynthesis: one coding for the aklavinone C-11 hydroxylase and the other corresponding to the putative dnrR2 regulatory gene of wild-type S. peucetius ATCC 29050 (K. J. Stutzman-Engwall, S. L. Otten, and C. R. Hutchinson, J. Bacteriol. 174:144-154, 1992). Northern (RNA) blot experiments, performed with a ric1 fragment containing daunorubicin-doxorubicin resistance gene(s), revealed a transcript of about 2,100 nucleotides that is present only during the phase of anthracycline metabolite production. The amount of this transcript is higher in strain 7600 than in strain 7900, a mutant which produces 5-fold more daunorubicin and 10-fold less doxorubicin than 7600. Furthermore, two 7900-derived blocked mutants, 8600 and 9700, do not express the 2,100-nucleotide transcript in spite of the absence of gross rearrangements in the ric1 region such as occur with the 7900 parental strain.