Dial 9-1-1 for DNA damage: the Rad9-Hus1-Rad1 (9-1-1) clamp complex

DNA Repair (Amst). Aug-Sep 2004;3(8-9):1009-14. doi: 10.1016/j.dnarep.2004.03.032.


Genotoxic stress activates checkpoint signaling pathways that block cell cycle progression, trigger apoptosis, and regulate DNA repair. Studies in yeast and humans have shown that Rad9, Hus1, Rad1, and Rad17 play key roles in checkpoint activation. Three of these proteins-Rad9, Hus1, and Rad1-interact in a heterotrimeric complex (dubbed the 9-1-1 complex), which resembles a PCNA-like sliding clamp, whereas Rad17 is part of a clamp-loading complex that is related to the PCNA clamp loader, replication factor-C (RFC). In response to genotoxic damage, the 9-1-1 complex is loaded around DNA by the Rad17-containing clamp loader. The DNA-bound 9-1-1 complex then facilitates ATR-mediated phosphorylation and activation of Chk1, a protein kinase that regulates S-phase progression, G2/M arrest, and replication fork stabilization. In addition to its role in checkpoint activation, accumulating evidence suggests that the 9-1-1 complex also participates in DNA repair. Taken together, these findings suggest that the 9-1-1 clamp is a multifunctional complex that is loaded onto DNA at sites of damage, where it coordinates checkpoint activation and DNA repair.

Publication types

  • Review

MeSH terms

  • Animals
  • Apoptosis
  • Cell Cycle
  • Cell Cycle Proteins / physiology*
  • Cell Division
  • DNA / chemistry
  • DNA / genetics
  • DNA Damage*
  • DNA Repair
  • DNA Repair Enzymes
  • DNA-Binding Proteins / metabolism
  • DNA-Binding Proteins / physiology*
  • Endonucleases / physiology*
  • Fungal Proteins / metabolism
  • G2 Phase
  • Humans
  • Models, Biological
  • Protein Binding
  • Replication Protein C
  • S Phase
  • Saccharomyces cerevisiae / physiology*
  • Saccharomyces cerevisiae Proteins
  • Schizosaccharomyces / physiology*
  • Schizosaccharomyces pombe Proteins
  • Signal Transduction
  • Time Factors


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • Schizosaccharomyces pombe Proteins
  • hus1 protein, S pombe
  • rad9 protein
  • DNA
  • Endonucleases
  • RAD1 protein, S cerevisiae
  • rad1 protein, S pombe
  • Replication Protein C
  • DNA Repair Enzymes