Differential regulation of homologous recombination at DNA breaks and replication forks by the Mrc1 branch of the S-phase checkpoint

EMBO J. 2009 Apr 22;28(8):1131-41. doi: 10.1038/emboj.2009.75. Epub 2009 Mar 26.


The Rad52 pathway has a central function in the recombinational repair of chromosome breaks and in the recovery from replication stress. Tolerance to replication stress also depends on the Mec1 kinase, which activates the DNA replication checkpoint in an Mrc1-dependent manner in response to fork arrest. Although the Mec1 and Rad52 pathways are initiated by the same single-strand DNA (ssDNA) intermediate, their interplay at stalled forks remains largely unexplored. Here, we show that the replication checkpoint suppresses the formation of Rad52 foci in an Mrc1-dependent manner and prevents homologous recombination (HR) at chromosome breaks induced by the HO endonuclease. This repression operates at least in part by impeding resection of DNA ends, which is essential to generate 3' ssDNA tails, the primary substrate of HR. Interestingly, we also observed that the Mec1 pathway does not prevent recombination at stalled forks, presumably because they already contain ssDNA. Taken together, these data indicate that the DNA replication checkpoint suppresses genomic instability in S phase by blocking recombination at chromosome breaks and permitting helpful recombination at stalled forks.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bleomycin / pharmacology
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Checkpoint Kinase 2
  • DNA Breaks*
  • DNA Repair
  • DNA Replication*
  • DNA, Fungal / drug effects
  • DNA, Fungal / genetics
  • DNA, Fungal / metabolism
  • Deoxyribonucleases, Type II Site-Specific / genetics
  • Deoxyribonucleases, Type II Site-Specific / metabolism
  • Hydroxyurea / pharmacology
  • Methyl Methanesulfonate / pharmacology
  • Models, Genetic
  • Mutagens / pharmacology
  • Protein Synthesis Inhibitors / pharmacology
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Rad51 Recombinase / genetics
  • Rad51 Recombinase / metabolism
  • Rad52 DNA Repair and Recombination Protein / genetics
  • Rad52 DNA Repair and Recombination Protein / metabolism
  • Recombination, Genetic*
  • S Phase / physiology*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Saccharomyces cerevisiae* / genetics
  • Saccharomyces cerevisiae* / metabolism


  • Cell Cycle Proteins
  • DNA, Fungal
  • MRC1 protein, S cerevisiae
  • Mutagens
  • Protein Synthesis Inhibitors
  • RAD52 protein, S cerevisiae
  • Rad52 DNA Repair and Recombination Protein
  • Saccharomyces cerevisiae Proteins
  • Bleomycin
  • Zeocin
  • Methyl Methanesulfonate
  • Checkpoint Kinase 2
  • Protein-Serine-Threonine Kinases
  • RAD53 protein, S cerevisiae
  • Rad51 Recombinase
  • HO protein, S cerevisiae
  • Deoxyribonucleases, Type II Site-Specific
  • Hydroxyurea