Essential for the control of the cell cycle at the G2/M (mitosis) transition. Interacts with the CDC2 protein kinase to form MPF. G2/M cyclins accumulate steadily during G2 and are abruptly destroyed at mitosis. Interacts with NAP1. Maximally expressed before mitosis. The levels peak late in the G2 phase of the cell cycle and are at a minimum in G1 phase. Present with 339 molecules/cell in log phase SD medium. Belongs to the cyclin family. Cyclin AB subfamily.