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      Sgs1 helicase and two nucleases Dna2 and Exo1 resect DNA double-strand break ends.

      Cell

      Adenosine Triphosphatases, metabolism, Animals, DNA Breaks, Double-Stranded, DNA Helicases, genetics, DNA Repair, Endodeoxyribonucleases, Exodeoxyribonucleases, Gene Conversion, Protein Structure, Tertiary, RecQ Helicases, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins

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          Abstract

          Formation of single-strand DNA (ssDNA) tails at a double-strand break (DSB) is a key step in homologous recombination and DNA-damage signaling. The enzyme(s) producing ssDNA at DSBs in eukaryotes remain unknown. We monitored 5'-strand resection at inducible DSB ends in yeast and identified proteins required for two stages of resection: initiation and long-range 5'-strand resection. We show that the Mre11-Rad50-Xrs2 complex (MRX) initiates 5' degradation, whereas Sgs1 and Dna2 degrade 5' strands exposing long 3' strands. Deletion of SGS1 or DNA2 reduces resection and DSB repair by single-strand annealing between distant repeats while the remaining long-range resection activity depends on the exonuclease Exo1. In exo1Deltasgs1Delta double mutants, the MRX complex together with Sae2 nuclease generate, in a stepwise manner, only few hundred nucleotides of ssDNA at the break, resulting in inefficient gene conversion and G2/M damage checkpoint arrest. These results provide important insights into the early steps of DSB repair in eukaryotes.

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          Author and article information

          Journal
          18805091
          2662516
          10.1016/j.cell.2008.08.037

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