Phosphorylation in cytosol Phosphorylation of Cdc2 by Wee1 in cytosol IEV:0001135 IMR:0100597 IMR:0100640 May act as a negative regulator of entry into mitosis (G2 to M transition) by protecting the nucleus from cytoplasmically activated cyclin B1-complexed CDC2 before the onset of mitosis. Its activity increases during S and G2 phases and decreases at M phase when it is hyperphosphorylated. A correlated decrease in protein level occurs at M/G1 phase, probably due to its degradation. Specifically phosphorylates and inactivates cyclin B1-complexed CDC2 reaching a maximum during G2 phase and a minimum as cells enter M phase. Phosphorylation of cyclin B1-CDC2 occurs exclusively on Tyr-15 and phosphorylation of monomeric CDC2 does not occur. CATALYTIC ACTIVITY: ATP + a protein tyrosine = ADP + protein tyrosine phosphate. Phosphorylation of Cdk1 by Wee1 in cytosol REACT:6178.2 REACT:6327.2 event Negative regulation of G2-M-phase transition