Wee1-like protein kinase (WEE1)

Acts as a negative regulator of entry into mitosis (G2 to M transition) by protecting the nucleus from cytoplasmically activated cyclin B1-complexed CDK1 before the onset of mitosis by mediating phosphorylation of CDK1 on'Tyr-15'. Specifically phosphorylates and inactivates cyclin B1-complexed CDK1 reaching a maximum during G2 phase and a minimum as cells enter M phase.

Phosphorylation of cyclin B1-CDK1 happens only on'Tyr-15' and phosphorylation of monomeric CDK1 doesn't occur. Its activity increases during S and G2 phases and decreases at M phase when it is hyperphosphorylated.