Cyclin A1 is involved in the control of the cell cycle at the G1/S (start) and G2/M (mitosis) transitions. Cyclin A1 is involved in the control of the control of the germline meiotic cell cycle and additionally in the control of mitotic cell cycle in some somatic cells. Cyclin A1 interacts with the CDK2 and the CDC2 protein kinases to form a serine/threonine kinase holoenzyme comple, Xenopus/Amphibian,. E, Xenopus/Amphibian,pression increases in early G1 phase and reaches highest levels during the S and G2/M phases.