The ability to convert carminomycin to daunorubicin can be conferred on a host by transforming the host with a recombinant vector comprising a DNA having the configuration of restriction sites shown in FIGS. 2, 3 & 4 and nucleotide sequence shown in FIG. 3 of the accompanying drawings or a restriction fragment derived therefrom containing a gene coding for carminomycin 4-O-methyltransferase.