Claspin, a novel protein required for the activation of Chk1 during a DNA replication checkpoint response in Xenopus egg extracts

Mol Cell. 2000 Oct;6(4):839-49. doi: 10.1016/s1097-2765(05)00092-4.


We have identified Claspin, a novel protein that binds to Xenopus Chk1 (Xchk1). Binding of Claspin to Xchk1 is highly elevated in the presence of DNA templates that trigger a checkpoint arrest of the cell cycle in Xenopus egg extracts. Xchk1 becomes phosphorylated during a checkpoint response, and we demonstrate directly that this phosphorylation results in the activation of Xchk1. Immunodepletion of Claspin from egg extracts abolishes both the phosphorylation and activation of Xchk1. Furthermore, Claspin-depleted extracts are unable to arrest the cell cycle in response to DNA replication blocks. Taken together, these findings indicate that Claspin is an essential upstream regulator of Xchk1.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Amino Acid Sequence
  • Animals
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Cycle / drug effects
  • Cell Cycle / physiology
  • Cell-Free System
  • Checkpoint Kinase 1
  • Cloning, Molecular
  • DNA Replication* / drug effects
  • Enzyme Activation
  • Female
  • Humans
  • Molecular Sequence Data
  • Oocytes / physiology*
  • Phosphorylation
  • Protein Kinases / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Templates, Genetic
  • Xenopus Proteins*
  • Xenopus laevis


  • Adaptor Proteins, Signal Transducing
  • CLSPN protein, Xenopus
  • CLSPN protein, human
  • Carrier Proteins
  • Recombinant Proteins
  • Xenopus Proteins
  • Protein Kinases
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • Chek1 protein, Xenopus

Associated data

  • GENBANK/AF297866
  • GENBANK/AF297867