Figure 1.

Two kinases are required to promote mitotic entry. Cyclin B-Cdk1 and Gwl are both required for mitotic entry. Cyclin B-Cdk1 is activated at G2-M by dephosphorylation of the inhibitory residues of Cdk1 threonine 14 and tyrosine 15 by the dual phosphatase Cdc25. Once activated, cyclin B-Cdk1 promotes phosphorylation of mitotic substrates. In contrast, Gwl activation at mitotic entry promotes the inhibition of PP2A-B55, the phosphatase responsible for mitotic substrate dephosphorylation. Dotted lines represent inactive pathways during mitosis. Dotted red lines symbolize indirect regulation.