title: Bidirectional resection of DNA double-strand breaks by Mre11 and Exo1.
abstract: Repair of DNA double-strand breaks (DSBs) by homologous recombination requires resection of 5'-termini to generate 3'-single-strand DNA tails. Key components of this reaction are exonuclease 1 and the bifunctional endo/exonuclease, Mre11 (refs 2-4). Mre11 endonuclease activity is critical when DSB termini are blocked by bound protein--such as by the DNA end-joining complex, topoisomerases or the meiotic transesterase Spo11 (refs 7-13)--but a specific function for the Mre11 3'-5' exonuclease activity has remained elusive. Here we use Saccharomyces cerevisiae to reveal a role for the Mre11 exonuclease during the resection of Spo11-linked 5'-DNA termini in vivo. We show that the residual resection observed in Exo1-mutant cells is dependent on Mre11, and that both exonuclease activities are required for efficient DSB repair. Previous work has indicated that resection traverses unidirectionally. Using a combination of physical assays for 5'-end processing, our results indicate an alternative mechanism involving bidirectional resection. First, Mre11 nicks the strand to be resected up to 300 nucleotides from the 5'-terminus of the DSB--much further away than previously assumed. Second, this nick enables resection in a bidirectional manner, using Exo1 in the 5'-3' direction away from the DSB, and Mre11 in the 3'-5' direction towards the DSB end. Mre11 exonuclease activity also confers resistance to DNA damage in cycling cells, suggesting that Mre11-catalysed resection may be a general feature of various DNA repair pathways.
authors: Genome Damage and Stability Centre, The University of Sussex, Brighton, BN1 9RQ, UK.
authors: Valerie
authors: V
authors: Garcia
authors: Sarah E L
authors: SE
authors: Phelps
authors: Stephen
authors: S
authors: Gray
authors: Matthew J
authors: MJ
authors: Neale
mesh_terms: D055162:Biocatalysis; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008540:Meiosis; D008954:Models, Biological; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D000099257:Meiotic Recombination Protein SPO11
chemical_list: D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; D029701:Saccharomyces cerevisiae Proteins; C094191:MRE11 protein, S cerevisiae; C518938:Spo11 protein, S cerevisiae; D000099257:Meiotic Recombination Protein SPO11; C028450:exodeoxyribonuclease I