Effects of photo-activated bleomycin on deoxyribonuclease I, exonuclease III and deoxyribonucleic acid polymerase I reactions.

The activity of bleomycin to break the strand of deoxyribonucleic acid (DNA) in the presence of 2-hydroxy-1-ethanethiol (2-mercaptoethanol) was enhanced by ultraviolet (UV) irradiation. Photo-activated bleomycin stimulated the action of deoxyribonuclease I (DNase I) to degrade DNA and the DNA synthesis by DNA polymerase I with DNase I. On the other hand, although UV-irradiated bleomycin scarcely broke the DNA strand in the presence of 1,2-benzenediol (catechol), it stimulated the action of DNase I to degrade DNA in the presence of catechol. In accordance with the inhibition by catechol, when DNA treated with UV-irradiated bleomycin in the presence of catechol was employed as a primer for the DNA synthesis, the incorporation of precursor into the acid-insoluble fraction by DNA polymerase I with exonuclease III was reduced to about one-half of the incorporation into DNA treated with unirradiated bleomycin. These findings suggest that the ability of bleomycin to bind to double-helical DNA forming regions sensitive to DNase I was increased by an appropriate dose of UV irradiation and that catechol inhibited the activity of the UV-irradiated bleomycin to break the DNA strand rather than to bind to DNA.