Essential for the control of the cell cycle at the G2/M (mitosis) transition. Interacts with the Cdk1 and Cdk2 protein kinases to form MPF. G2/M cyclins accumulate steadily during G2 and are abruptly destroyed at mitosis. Component of the Frs-CycA-Cdk1 complex composed of CycA, Cdk1 and Z600. Interacts (via C-terminus) with Z600. Belongs to the cyclin family. Cyclin AB subfamily.