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Letter

Nature Cell Biology 5, 161–165 (1 February 2003) | doi:10.1038/ncb921

Repeated phosphopeptide motifs in Claspin mediate the regulated binding of Chk1

Akiko Kumagai & William G. Dunphy

In vertebrates, the checkpoint-regulatory kinase Chk1 mediates cell-cycle arrest in response to a block in DNA replication or to DNA damaged by ultraviolet radiation. The activation of Chk1 depends on both Claspin and the upstream regulatory kinase ATR.