Essential for the control of the cell cycle at the G2/M (mitosis) transition. G2/M cyclins accumulate steadily during G2 and are abruptly destroyed at mitosis. Interacts with the CDC2 and CDK2 protein kinases to form a serine/threonine kinase holoenzyme complex. The cyclin subunit imparts substrate specificity to the complex. Accumulates steadily during G2 and is abruptly destroyed at mitosis. Belongs to the cyclin family. Cyclin AB subfamily.