Claspin (CLSPN)

Claspin localized in nuclei and associated with CHK1 following replication stress or other types of DNA damage. Claspin was phosphorylated in response to replication stress, and phosphorylation appeared to be required for the association between claspin and CHK1. In addition, claspin interacted with the checkpoint proteins ATR and RAD9. Since ATR and the RAD9-RAD1-HUS1 complex are involved in CHK1 activation, the authors hypothesized that claspin may be an adaptor that brings these molecules together. Downregulation of claspin by small interfering RNA inhibited CHK1 activation in response to replication stress, augmented the premature chromatin condensation induced by hydroxyurea, inhibited ultraviolet-induced reduction of DNA synthesis, and decreased cell survival.