CHEK1(Checkpoint kinase-1) is also named as CHK1 and belongs to the protein kinase superfamily. It is implicated in a circuit in which it activates checkpoints,DNA repair and proliferating cell nuclear antigen and FANCD2 monoubiquitinylation. CHEK1 protects vertebrate cells against spontaneous chromosome missegregation and is required to sustain anaphase delay when spindle function is disrupted by taxol. It has 3 isoforms produced by alternative splicing with the molecular mass of 54 kDa,44 kDa and 50 kDa.