Cyclin A was the first cyclin cloned, and mammalian cells express two A-type cyclins, A1 and A2. Cyclin A1 is expressed almost exclusively in the testes, during meiosis in the male germline, whereas cyclin A2 is ubiquitously expressed in all proliferating cells and is generally considered to be the mammalian S phase cyclin. During cell cycle progression, cyclin A2 is induced at the beginning of the S phase. Once induced, cyclin A2 binds and activates its catalytic partners, cyclin-dependent kinases Cdk2 and Cdk1. These cyclin A2-Cdk complexes phosphorylate critical proteins that play a role in DNA synthesis, thereby driving S phase progression. Cyclin A2 is expressed throughout the S and G2 phases and is rapidly degraded upon entry of cells into mitosis. An essential function for cyclin A in cell proliferation is supported by the observations that cyclin A2 knockout mouse embryos died shortly after implantation. These studies have led to the current model that the core components of the cell cycle machinery (cyclins A and B) are essential elements of the cell cycle engine.
Anti-Human CyclinA (BF683)-158Gd—50 Tests