Claspin: Proteins and Enzymes

Claspin is a nuclear protein whose expression peaks during S and G2 phases of the cell cycle. Claspin is phosphorylated by ATR in response to DNA damage or replication stress. Phosphorylated Claspin associates with Chk1 via three CKB motifs, and regulates the ATR-dependent phosphorylation and activation of Chk1. Deficits in Claspin expression are associated with failure to undergo cell cycle arrest in response to DNA damage.