title: The role of DNA double-strand breaks in spontaneous homologous recombination in S. cerevisiae.
abstract: Homologous recombination (HR) is a source of genomic instability and the loss of heterozygosity in mitotic cells. Since these events pose a severe health risk, it is important to understand the molecular events that cause spontaneous HR. In eukaryotes, high levels of HR are a normal feature of meiosis and result from the induction of a large number of DNA double-strand breaks (DSBs). By analogy, it is generally believed that the rare spontaneous mitotic HR events are due to repair of DNA DSBs that accidentally occur during mitotic growth. Here we provide the first direct evidence that most spontaneous mitotic HR in Saccharomyces cerevisiae is initiated by DNA lesions other than DSBs. Specifically, we describe a class of rad52 mutants that are fully proficient in inter- and intra-chromosomal mitotic HR, yet at the same time fail to repair DNA DSBs. The conclusions are drawn from genetic analyses, evaluation of the consequences of DSB repair failure at the DNA level, and examination of the cellular re-localization of Rad51 and mutant Rad52 proteins after introduction of specific DSBs. In further support of our conclusions, we show that, as in wild-type strains, UV-irradiation induces HR in these rad52 mutants, supporting the view that DNA nicks and single-stranded gaps, rather than DSBs, are major sources of spontaneous HR in mitotic yeast cells.
authors.affiliation: Center for Microbial Biotechnology, BioCentrum-DTU, Technical University of Denmark, Lyngby, Denmark.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Lettier
authors.forename: Qi
authors.initials: Q
authors.lastname: Feng
authors.forename: Adriana Antúnez
authors.initials: AA
authors.lastname: de Mayolo
authors.forename: Naz
authors.initials: N
authors.lastname: Erdeniz
authors.forename: Robert J D
authors.initials: RJ
authors.lastname: Reid
authors.forename: Michael
authors.initials: M
authors.lastname: Lisby
authors.forename: Uffe H
authors.initials: UH
authors.lastname: Mortensen
authors.forename: Rodney
authors.initials: R
authors.lastname: Rothstein
mesh_terms: D000483:Alleles; D002166:Camptothecin / Q000494:pharmacology; D015825:Chromosomes, Fungal / Q000235:genetics / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D026942:DNA Topoisomerases / Q000378:metabolism; D004271:DNA, Fungal / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005720:Gamma Rays; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008938:Mitosis / Q000187:drug effects / Q000502:physiology; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D021381:Protein Transport / Q000187:drug effects; D051135:Rad51 Recombinase / Q000378:metabolism; D051721:Rad52 DNA Repair and Recombination Protein / Q000378:metabolism; D011995:Recombination, Genetic / Q000235:genetics* / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D050505:Mutant Proteins; C497197:RAD52 protein, S cerevisiae; C400213:RAD59 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; C495151:RAD51 protein, S cerevisiae; D051135:Rad51 Recombinase; D026942:DNA Topoisomerases; D002166:Camptothecin