CCNA2 belongs to the highly conserved cyclin family,whose members are characterized by a dramatic periodicity in protein abundance through the cell cycle. Cyclins function as regulators of CDK kinases. Different cyclins exhibit distinct expression and degradation patterns which contribute to the temporal coordination of each mitotic event. In contrast to cyclin A1,which is present only in germ cells,this cyclin is expressed in all tissues tested. CCNA2 binds and activates CDC2 or CDK2 kinases,and thus promotes both cell cycle G1/S and G2/M transitions.