Essential for the control of the cell cycle at the G2/M (mitosis) transition (PubMed:2847913, PubMed:2908246). Interacts with the cdc2 protein kinase to form MPF (PubMed:8455610). G2/M cyclins accumulate steadily during G2 and are abruptly destroyed at mitosis (PubMed:2534559). Involved in the reorganization of the cytoskeleton on transition from G2 to mitosis (PubMed:2908246). Association with rum1 promotes its proteolysis during G1 (PubMed:9303310). Also essential for initiation of meiosis II (PubMed:7498766). Interacts with cdc2 (PubMed:8455610). Interacts with rum1 (PubMed:9303310, PubMed:9472012, PubMed:9614176). Associates with microtubules (PubMed:2847913). Also interacts with cdc11 (PubMed:15062098). Belongs to the cyclin family. Cyclin AB subfamily.