Structure of bleomycin-induced DNA double-strand breaks: predominance of blunt ends and single-base 5' extensions.
In order to examine the structure of bleomycin-induced DNA double-strand breaks, defined-sequence DNA was labeled in each strand at a single restriction site and treated with bleomycin. Various double-stranded fragments resulting from bleomycin-induced double-strand breaks were isolated, denatured, and run on sequencing gels to determine the sites of cleavage in each strand. For virtually every double-strand break, the cleavage site in one strand was a pyrimidine in a G-Py sequence, reflecting a specificity similar to that of bleomycin-induced single-strand cleavage. However, the cleavage site in the complementary strand was seldom a G-Py sequence, and was usually a site where single-strand cleavage was infrequent. When the sequence at the double-strand break was G-Py-Py', the break at Py was usually accompanied by a break at the base directly opposite Py, resulting in blunt ends. When the sequence was G-Py-Pu, the break at Py was usually accompanied by a break at the base opposite Pu, resulting in single-base 5' extensions. Double-strand breaks with 3' extensions, such as would result from cleavage of two C residues in a self-complementary G-C sequence, were conspicuously absent. These data provide further evidence that bleomycin-induced double-strand breaks do not result from coincidence of independent site-specific single-strand breaks.(ABSTRACT TRUNCATED AT 250 WORDS)
Povirk
L F
LF
Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
Han
Y H
YH
Steighner
R J
RJ
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001483:Base Sequence; D001665:Binding Sites; D001761:Bleomycin / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D008954:Models, Biological
D000903:Antibiotics, Antineoplastic; D001761:Bleomycin; D004247:DNA