Has a role in the DNA replication-monitoring S/G2 checkpoint system. It is responsible for blocking mitosis in the S phase. It monitors DNA synthesis by interacting with DNA polymerase alpha and sends a signal to block the onset of mitosis while DNA synthesis is in progress. Phosphorylates rad60 and dna2. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with rad26. Autophosphorylated. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. CHEK2 subfamily.