Catalytic domain of the Serine/Threonine Kinase, Cell Division Cycle 7 kinase
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Cdc7 kinase (or Hsk1 in fission yeast) is a critical regulator in the initiation of DNA replication. It forms a complex with a Dbf4-related regulatory subunit, a cyclin-like molecule that activates the kinase in late G1 phase, and is also referred to as Dbf4-dependent kinase (DDK). Its main targets are mini-chromosome maintenance (MCM) proteins. Cdc7 kinase may also have additional roles in meiosis, checkpoint responses, the maintenance and repair of chromosome structures, and cancer progression. The Cdc7 kinase subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.