ANALYSIS OF CLUSTERED GENES ENCODING BOTH EARLY AND LATE STEPS IN DAUNOMYCIN BIOSYNTHESIS BY STREPTOMYCES SP STRAIN C5

We recently described the isolation and sequence analysis of the dauno mycin polyketide synthase biosynthesis genes of Streptomyces sp, strai n C5 (J, Ye, M, L, Dickens, R, Plater, Y, Li, J, Lawrence, and W, R, S trohl, J, Bacteriol, 176:6270-6280, 1994), Contiguous to the daunomyci n polyketide synthase biosynthesis gene region in Streptomyces sp. str ain C5 are four additional genes involved in daunomycin biosynthesis, two of the products of which show similarity to different types of met hyltransferases, The dauC gene, encoding aklanonic acid methyltransfer ase (AAMT), complements dauC-blocked mutants of Streptomyces sp, strai n C5, restores in vitro AAMT activities to the mutant strains, and con fers in vitro AAMT activity on Streptomyces lividans, Partial purifica tion through gel filtration, followed by photoaffinity labeling of enr iched AAMT with S-adenosyl-L-[H-3-methyl]methionine, indicates that AA MT is a homodimer with an M, of ca, 48,000 (subunit M, of ca, 24,000), which corresponds with the size of the deduced gene product, The dauD gene, encoding aklanonic acid methyl ester cyclase, is divergently ar ranged with respect to dauC, Immediately downstream and apparently tra nslationally coupled with dauD is the dauK gene, encoding carminomycin 4-O-methyltransferase. The dauK gene confers in vitro carminomycin 4- O-methyltransferase activity on S, lividans and is nearly identical to a similar gene isolated from Streptomyces peucetius and characterized , Directly downstream of dauK lies a gene encoding a deduced protein t hat is similar to the methyl esterases.