Bidirectional resection of DNA double-strand breaks by Mre11 and Exo1

• Published in: Nature (London) Vol. 479; no. 7372; pp. 241 - 244
• Main Authors: Garcia, Valerie, Phelps, Sarah E. L., Gray, Stephen, Neale, Matthew J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 10.11.2011; Nature Publishing Group
• Subjects: 631/337/1427/2122; 631/337/1427/2190; 631/337/1427/2191; 631/45/607/1159; Biocatalysis; Chemical properties; Deoxyribonucleic acid; DNA; DNA Breaks, Double-Stranded; DNA Repair; Endodeoxyribonucleases - genetics; Endodeoxyribonucleases - metabolism; Exodeoxyribonucleases - deficiency; Exodeoxyribonucleases - genetics; Exodeoxyribonucleases - metabolism; Exonucleases; Genetic aspects; Humanities and Social Sciences; letter; Meiosis; Methods; Models, Biological; multidisciplinary; Mutation; Proteins; Saccharomyces cerevisiae - cytology; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Science; Science (multidisciplinary); United States
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10515

DNA strand-break removal by Mre11 and Exo1 Specific DNA double-strand breaks are made during meiosis by Spo11, which remains bound to the DNA ends. Mre11 is a nuclease that can act exonucleolytically at DNA ends and endonucleolytically at internal sites. Previous studies have defined a role for the endonuclease, but not exonuclease, activity in DNA repair. Matthew Neale and colleagues show that Mre11 first makes a nick 300 bases from the end of the 5' strand, after which Mre11 degrades the DNA towards the break. Meanwhile, a second nuclease, Exo1, degrades the same strand in the opposite direction. This demonstrates that exonucleases can be loaded when the DNA end that is usually required for their initial binding is blocked. Repair of DNA double-strand breaks (DSBs) by homologous recombination requires resection of 5′-termini to generate 3′-single-strand DNA tails 1 . 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 5 , topoisomerases 6 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 1 . 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.