title: Yeast recombination pathways triggered by topoisomerase II-mediated DNA breaks.
abstract: Topoisomerase II is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating transient double-strand DNA breaks. While the enzyme cannot perform its essential cellular functions without cleaving DNA, this scission activity is inherently dangerous to chromosomal integrity. In fact, etoposide and other clinically important anticancer drugs kill cells by increasing levels of topoisomerase II-mediated DNA breaks. Cells rely heavily on recombination to repair double-strand DNA breaks, but the specific pathways used to repair topoisomerase II-generated DNA damage have not been defined. Therefore, Saccharomyces cerevisiae was used as a model system to delineate the recombination pathways that repair DNA breaks generated by topoisomerase II. Yeast cells that expressed wild-type or a drug-hypersensitive mutant topoisomerase II or overexpressed the wild-type enzyme were examined. Based on cytotoxicity and recombination induced by etoposide in different repair-deficient genetic backgrounds, double-strand DNA breaks generated by topoisomerase II appear to be repaired primarily by the single-strand invasion pathway of homologous recombination. Non-homologous end joining also was triggered by etoposide treatment, but this pathway was considerably less active than single-strand invasion and did not contribute significantly to cell survival in S.cerevisiae.
authors.affiliation: Department of Biochemistry,Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Sabourin
authors.forename: John L
authors.initials: JL
authors.lastname: Nitiss
authors.forename: Karin C
authors.initials: KC
authors.lastname: Nitiss
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tatebayashi
authors.forename: Hideo
authors.initials: H
authors.lastname: Ikeda
authors.forename: Neil
authors.initials: N
authors.lastname: Osheroff
mesh_terms: D002453:Cell Cycle; D002455:Cell Division / Q000187:drug effects; D004249:DNA Damage; D004260:DNA Repair; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D005047:Etoposide / Q000633:toxicity; D008957:Models, Genetic; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development
chemical_list: D005047:Etoposide; D004250:DNA Topoisomerases, Type II