Nonspecific cleavage of .vphi.X174 RFI deoxyribonucleic acid by bleomycin

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Abstract
The covalently closed circular duplex DNA of [bacteriophage] .vphi.X174 underwent progressive conversion to nicked and linear DNA with increasing bleomycin[an antineoplastic drug] .vphi.X174 RFI DNA molecule ratios. The formation of linear DNA (a double-strand break) occurred under limited reaction conditions as low as an average of 0.2 single-strand break/.vphi.X174 RFI DNA molecule. As bleomycin-produced linear DNA was further fragmented by bleomycin, a broad distribution of DNA fragments without notable concentrations of unique size was formed. Restriction enzymes PstI and SstII did not generate discrete fragments from bleomycin-produced full-length linear .vphi.X174 DNA, nor did bleomycin cleavage generate discrete fragments from HpaII or PstI digests of .vphi. X174 RFI. Bleomycin probably does not act at a few specific sites on .vphi.X174 RFI DNA. The single-strand nick appeared to be the preferred site for bleomycin action for a 2nd cleavage in a .vphi.X174 molecule.