Background：

Serine/threonine-protein kinase involved in the control of the cell cycle; essential for meiosis， but dispensable for mitosis. Phosphorylates CTNNB1， USP37， p53/TP53， NPM1， CDK7， RB1， BRCA2， MYC， NPAT， EZH2. Triggers duplication of centrosomes and DNA. Acts at the G1-S transition to promote the E2F transcriptional program and the initiation of DNA synthesis， and modulates G2 progression; controls the timing of entry into mitosis/meiosis by controlling the subsequent activation of cyclin B/CDK1 by phosphorylation， and coordinates the activation of cyclin B/CDK1 at the centrosome and in the nucleus. Crucial role in orchestrating a fine balance between cellular proliferation， cell death， and DNA repair in human embryonic stem cells (hESCs). Activity of CDK2 is maximal during S phase and G2; activated by interaction with cyclin E during the early stages of DNA synthesis to permit G1-S transition， and subsequently activated by cyclin A2 (cyclin A1 in germ cells) during the late stages