Cdk1Ciklin

CDK1-Cyclin, often referred to as the CDK1–Cyclin complex, is a central driver of the eukaryotic cell cycle, with particular importance for the transition from G2 phase into mitosis. In many organisms, CDK1 is the essential catalytic subunit, while cyclins provide regulatory input that dictates when the kinase is active. The classic mitotic partner is Cyclin B, but CDK1 can associate with other cyclins in different cellular contexts, contributing to various cell-cycle events.

Activation and regulation of the complex rely on phosphorylation states. A CDK-activating kinase (CAK) phosphorylates CDK1 at a threonine residue to promote activity. Inhibitory phosphorylation on Thr14 and Tyr15 by Wee1 or Myt1 kinases keeps CDK1 inactive until the appropriate time. Cdc25 phosphatases remove these inhibitory phosphates to unleash kinase activity as cells enter mitosis. Cyclin B levels rise during G2, enabling MPF formation; shortly after mitosis begins, the anaphase-promoting complex/cyclosome (APC/C) targets Cyclin B for degradation, reducing CDK1 activity and allowing mitotic exit.

CDK1–Cyclin targets a broad set of substrates to drive mitotic events, including nuclear envelope breakdown, chromosome condensation, spindle assembly, and cytokinesis. The complex is highly conserved and essential for cell division across eukaryotes; loss or malfunction typically results in cell-cycle arrest or cell death. The concept of MPF reflects the idea that CDK1–Cyclin activity acts as a switch governing the initiation and progression of mitosis.