Claspin and Chk1 regulate replication fork stability by different mechanisms

Cell Cycle. 2009 Apr 1;8(7):1036-43. doi: 10.4161/cc.8.7.8040. Epub 2009 Apr 2.


The checkpoint mediator protein Claspin facilitates the phosphorylation and activation of Chk1 by ATR and thus is required for efficient DNA replication. However, the physical association of Claspin homologues with replication factors and forks suggests that it might have additional functions in controlling DNA replication. DNA combing was used to examine the functions of Chk1 and Claspin at individual forks and to determine whether Claspin functions independently of Chk1. We find that Claspin, like Chk1, regulates fork stability and density in unperturbed cells. As expected, Chk1 regulates origin firing predominantly by controlling Cdk2-Cdc25 function. By contrast, Claspin functions independently of the Cdc25-Cdk2 pathway in mammalian cells. The findings support a model in which Claspin plays a role regulating replication fork stability that is independent of its function in mediating Chk1 phosphorylation.

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Checkpoint Kinase 1
  • Cyclin-Dependent Kinase 2 / metabolism*
  • DNA Replication*
  • HeLa Cells
  • Humans
  • Phosphorylation
  • Protein Kinases / genetics
  • Protein Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • cdc25 Phosphatases / metabolism*


  • Adaptor Proteins, Signal Transducing
  • CLSPN protein, human
  • RNA, Small Interfering
  • Protein Kinases
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • cdc25 Phosphatases