Baumycin-negative mutants of Streptomyces coeruleorubidus ME130-A4 do not convert daunomycinone to daunomycin and baumycins. They biosynthesize daunomycin from aklavinone and epsilon-rhodomycinone, indicating the glycosidation of the aglycone before the synthesis of daunomycinone. The biosynthetic pathway from epsilon-rhodomycinone to daunomycin was further confirmed by studying the bioconversion of anthracyclinones and anthracyclines, which are presumed to be intermediates.