Specificity of DNA base release by bleomycin.

DNA was treated with bleomycin in the presence of Fe2+ and 2-mercaptoethanol under conditions where only a few percent of the bases were released. Release of all four bases was a linear function of bleomycin concentration, but the amount of thymine released was twice that of cytosine, 7 times that of adenine, and twelve times that of guanine. Unidentified minor products of thymine, of cytosine and of a purine were also released. Bromouracil did not sensitize DNA to bleomycin-induced breakage, and was released at the same rate as thymine.