Treatment of B-form DNA with the antitumor antibiotic bleomycin in the presence of Fe2+ and O2 affords both DNA strand scission and the formation of alkali-labile lesions, the proportion of which is quite sensitive to the concentration of O2 present. The alkali-labile lesions can undergo fragmentation cleanly in the presence of n-butylamine to afford DNA fragments containing 5'-and 3'-phosphate termini at the site of the alkali-labile lesion. The ...