Contribution of topoisomerase I to conversion of single-strand into double-strand DNA breaks.
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.
Kowalska-Loth
B
B
Institute of Biochemistry, Warsaw University, Poland.
Bubko
I
I
Komorowska
B
B
Szumiel
I
I
Staron
K
K
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
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