Cyclin which controls both the G1/S and the G2/M transition phases of the cell cycle. Functions through the formation of specific serine/threonine kinase holoenzyme complexes with the cyclin-dependent protein kinases CDK1 and CDK2. The cyclin subunit confers the substrate specificity of these complexes and differentially interacts with and activates CDK1 and CDK2 throughout the cell cycle. Interacts with the CDK1 and CDK2 protein kinases to form serine/threonine kinase holoenzyme complexes. Interacts with CDK1 (hyperphosphorylated form in G1 and underphosphorylated forms in S and G2). Interacts with CDK2; the interaction increases from G1 to G2. Interacts (associated with CDK2 but not with CDK1) with SCAPER; regulates the activity of CCNA2/CDK2 by transiently maintaining CCNA2 in the cytoplasm. Forms a ternary complex with CDK2 and CDKN1B; CDKN1B inhibits the kinase activity of CDK2 through conformational rearrangements. Interacts with INCA1. Exclusively nuclear during interphase. Detected in the nucleus and the cytoplasm at prophase. Cytoplasmic when associated with SCAPER. Polyubiquitinated via 'Lys-11'-linked ubiquitin by the anaphase-promoting complex (APC/C), leading to its degradation by the proteasome. Deubiquitinated and stabilized by USP37 enables entry into S phase. Belongs to the cyclin family. Cyclin AB subfamily.