title: The basis for camptothecin enhancement of DNA breakage by eukaryotic topoisomerase I.
abstract: The eukaryotic topoisomerase I (topo I) is the target of the cytotoxic alkaloid camptothecin (CTT). In vitro, CTT enhances the breakage of DNA by topo I when the reaction is stopped with detergent. Although breakage at some sites is enhanced to a great extent while breakage at others is enhanced only minimally, CTT does not significantly change the breakage specificity of topo I in vitro. It has been suggested that CTT acts by slowing the reclosure step of the nicking-closing reaction. To test this hypothesis, we have measured the rate of reclosure for different break sites in the presence of CTT after adding 0.5 M NaCl to a standard low salt reaction. In support of the hypothesis, we find that topo I-mediated DNA breakage is enhanced the greatest at those sites where closure of the break is the slowest. These results suggest a mechanism for the toxicity of CTT in vivo.
authors.affiliation: Department of Microbiology, University of Washington, Seattle 98195.
authors.forename: S E
authors.initials: SE
authors.lastname: Porter
authors.forename: J J
authors.initials: JJ
authors.lastname: Champoux
mesh_terms: D000818:Animals; D001483:Base Sequence; D002166:Camptothecin / Q000494:pharmacology*; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004279:DNA, Viral / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D051381:Rats; D013539:Simian virus 40 / Q000378:metabolism; D012965:Sodium Chloride; D014908:Triticum / Q000201:enzymology
chemical_list: D004279:DNA, Viral; D012965:Sodium Chloride; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin