The product of this gene is an essential upstream regulator of checkpoint kinase 1 and triggers a checkpoint arrest of the cell cycle in response to replicative stress or DNA damage. The protein is also required for efficient DNA replication during a normal S phase. Multiple transcript variants encoding different isoforms have been found for this gene.,CLSPN,claspin,Epigenetics & Nuclear Signaling,DNA Damage & Repair,Cell Biology & Developmental Biology,Cell Cycle,Cell cycle inhibitors,CLSPN