title: Contribution of topoisomerase I to conversion of single-strand into double-strand DNA breaks.
abstract: An in vitro system composed of nicked pBR322 DNA and purified topoisomerase I was employed to study the efficiency of the topoisomerase I-driven single-strand to double-strand DNA breaks conversion. At 1.4 x 10(5) topoisomerase I activity units per mg DNA about 20% single-strand nicks were converted into double-strand breaks during 30 min due to topoisomerase I action. Camptothecin inhibited the conversion. The conversion was also inhibited when the relaxing activity of the used topoisomerase I was increased by phosphorylation of the enzyme with casein kinase 2. The presented data suggest that topoisomerase I may be involved in production of double-stranded breaks in irradiated cells and that this process positively depends on the amount of topoisomerase I but not on its phosphorylation state.
authors.affiliation: Institute of Biochemistry, Warsaw University, Poland.
authors.forename: B
authors.initials: B
authors.lastname: Kowalska-Loth
authors.forename: I
authors.initials: I
authors.lastname: Bubko
authors.forename: B
authors.initials: B
authors.lastname: Komorowska
authors.forename: I
authors.initials: I
authors.lastname: Szumiel
authors.forename: K
authors.initials: K
authors.lastname: Staron
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology; D047390:Casein Kinase II; D002417:Cattle; D004247:DNA / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism; D005720:Gamma Rays; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004247:DNA; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin