title: DNA resection at chromosome breaks promotes genome stability by constraining non-allelic homologous recombination.
abstract: DNA double-strand breaks impact genome stability by triggering many of the large-scale genome rearrangements associated with evolution and cancer. One of the first steps in repairing this damage is 5'→3' resection beginning at the break site. Recently, tools have become available to study the consequences of not extensively resecting double-strand breaks. Here we examine the role of Sgs1- and Exo1-dependent resection on genome stability using a non-selective assay that we previously developed using diploid yeast. We find that Saccharomyces cerevisiae lacking Sgs1 and Exo1 retains a very efficient repair process that is highly mutagenic to genome structure. Specifically, 51% of cells lacking Sgs1 and Exo1 repair a double-strand break using repetitive sequences 12-48 kb distal from the initial break site, thereby generating a genome rearrangement. These Sgs1- and Exo1-independent rearrangements depend partially upon a Rad51-mediated homologous recombination pathway. Furthermore, without resection a robust cell cycle arrest is not activated, allowing a cell with a single double-strand break to divide before repair, potentially yielding multiple progeny each with a different rearrangement. This profusion of rearranged genomes suggests that cells tolerate any dangers associated with extensive resection to inhibit mutagenic pathways such as break-distal recombination. The activation of break-distal recipient repeats and amplification of broken chromosomes when resection is limited raise the possibility that genome regions that are difficult to resect may be hotspots for rearrangements. These results may also explain why mutations in resection machinery are associated with cancer.
authors.affiliation: Howard Hughes Medical Institute and Department of Embryology, Carnegie Institution, Baltimore, Maryland, United States of America.
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Tan
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Hoang
authors.forename: Douglas
authors.initials: D
authors.lastname: Koshland
mesh_terms: D000483:Alleles; D059447:Cell Cycle Checkpoints; D019457:Chromosome Breakage; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004171:Diploidy; D005090:Exodeoxyribonucleases / Q000235:genetics; D015321:Gene Rearrangement; D016681:Genome, Fungal; D042822:Genomic Instability; D059765:Homologous Recombination / Q000235:genetics; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism; D053484:RecQ Helicases / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C495151:RAD51 protein, S cerevisiae; D051135:Rad51 Recombinase; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; C090472:SGS1 protein, S cerevisiae; D053484:RecQ Helicases