title: Effects of uracil incorporation, DNA mismatches, and abasic sites on cleavage and religation activities of mammalian topoisomerase I.
abstract: Abasic sites and deamination of cytosine to uracil are probably the most common types of endogenous DNA damage. The effects of such lesions on DNA topoisomerase I (top1) activity were examined in oligonucleotides containing a unique top1 cleavage site. The presence of uracils and abasic sites within the first 4 bases immediately 5' to the cleavage site suppressed normal top1 cleavage and induced new top1 cleavage sites. Uracils immediately 3' to the cleavage site increased cleavage and produced a camptothecin mimicking effect. A mismatch with a bulge or abasic sites immediately 3' to the top1 cleavage site irreversibly trapped top1 cleavable complexes in the absence of camptothecin and produced a suicide cleavage complex. These results demonstrate that top1 activity is sensitive to physiological, environmental, and pharmacological DNA modifications and that top1 can act as a specific mismatch- and abasic site-nicking enzyme.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Basic Sciences, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: P
authors.initials: P
authors.lastname: Pourquier
authors.forename: L M
authors.initials: LM
authors.lastname: Ueng
authors.forename: G
authors.initials: G
authors.lastname: Kohlhagen
authors.forename: A
authors.initials: A
authors.lastname: Mazumder
authors.forename: M
authors.initials: M
authors.lastname: Gupta
authors.forename: K W
authors.initials: KW
authors.lastname: Kohn
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D000818:Animals; D001665:Binding Sites; D004247:DNA / Q000235:genetics*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006868:Hydrolysis; D008322:Mammals; D009692:Nucleic Acid Heteroduplexes; D014498:Uracil / Q000378:metabolism*
chemical_list: D009692:Nucleic Acid Heteroduplexes; D014498:Uracil; D004247:DNA; D004264:DNA Topoisomerases, Type I