CDK1cyclin

Cdk1cyclin refers to the heterodimeric complex formed by CDK1 and a regulatory cyclin, most prominently Cyclin B, which constitutes the M-phase promoting factor (MPF) that triggers entry into mitosis in animal cells and many eukaryotes.

CDK1 is a serine/threonine kinase. Activation requires binding to cyclin and phosphorylation at Thr161 by a CDK-activating kinase; binding to cyclin relieves auto-inhibition. Cyclin levels rise during the cell cycle, with Cyclin B peaking in G2/M. The activity is further regulated by phosphorylation: Wee1-family kinases phosphorylate CDK1 on Tyr15 and Thr14 (inhibitory), while Cdc25 phosphatases remove these phosphates to activate.

The activated CDK1-cyclin complex drives mitotic entry by phosphorylating substrates that promote nuclear envelope breakdown, chromosome condensation, spindle formation, and other mitotic events. Cyclin B is then targeted for destruction by the anaphase-promoting complex/cyclosome (APC/C), leading to CDK1 inactivation and mitotic exit.

In multicellular organisms, CDK1-cyclin complexes are essential for cell proliferation; dysregulation can contribute to oncogenesis. The complex is a common target in research, with various inhibitors used to study cell cycle control.