May be involved in the control of the cell cycle at the G1/S (start) and G2/M (mitosis) transitions. May primarily function in the control of the germline meiotic cell cycle and additionally in the control of mitotic cell cycle in some somatic cells. Interacts with INCA1 and KLHDC9 (By similarity). Interacts with the CDK2 and CDC2 protein kinases to form a serine/threonine kinase holoenzyme complex. The cyclin subunit imparts substrate specificity to the complex. Found in a complex with CDK2, CABLES1 and CCNE1. In oocytes at least, it associates with the spindle during metaphase. Testis and ovaries. In male germ cells just prior to or during the first, but not the second meiotic division. 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 (By similarity). CCNA1 -/- males are sterile due to a block of spermatogenesis before the first meiotic division, whereas females are normal. Belongs to the cyclin family. Cyclin AB subfamily.