Topoisomerase II activity in a DNA double-strand break repair deficient Chinese hamster ovary cell line

Raymond L. Warters, Bradley W. Lyons, T. Mua Li, David J. Chen

Research output: Contribution to journalArticle

16 Scopus citations


Topoisomerase II activity was measured in wild-type, Chinese hamster ovary K1 cells, and in the DNA double-strand break repair deficient xrs-6 cell line. Total topoisomerase II activity in a high salt, nuclear extract was found to be the same in both cell lines, as measured by decatenation of kinetoplast DNA networks and catenation of plasmid pBr322 DNA. While at low drug concentrations m-AMSA-induced enzyme cutting of nuclear DNA was 25% less in xrs-6 cells, the frequency of DNA breaks at high concentrations of the drug, and thus the frequency of the topoisomerase II enzyme, was the same in both cell lines. Despite the presence of equivalent enzyme levels in both cell lines, the xrs-6 cell line was 3 times more sensitive to drug-induced cytotoxicity. These results may be due to the fact that, as with X-radiation-induced DNA damage, xrs-6 cells are deficient in the capacity to rejoin topoisomerase II-induced DNA double-strand breaks.

Original languageEnglish (US)
Pages (from-to)167-174
Number of pages8
JournalMutation Research-DNA Repair
Issue number2
Publication statusPublished - 1991



  • Chinese hamster ovary cell line
  • DNA double-strand break repair
  • Topoisomerase II

ASJC Scopus subject areas

  • Genetics
  • Molecular Biology
  • Toxicology

Cite this