PKs catalyse the transfer of the gamma-phosphoryl group from ATP to serine/threonine or tyrosine residues on protein substrates. This entry includes Wee1 from Arabidopsis. Wee1 is a cell cycle checkpoint kinase that is involved in the regulation of cyclin-dependent kinase CDK1, the master engine for mitosis [, ]. It has been shown that Arabidopsis Wee1 directly interacts with and phosphorylates the E3 ubiquitin ligase FBL17 that promotes the degradation of CDK inhibitors [].
This entry includes cell division cycle-associated protein 3 (CDCA3; also known as trigger of mitotic entry protein 1 or TOME-1), which is required for entry into mitosis. The protein is found at high levels during the G2 and M phases of mitosis, but declines rapidly during the G2 phase. Entry into mitosis requires the relocalization to the nucleus and activation of cyclin-dependent kinase 1 (cdk1) by association with cyclin B, and exit from mitosis occurs when cyclin B is degraded and the kinase activity decreases. Anaphase promoting complex (APC) is an E3 ligase active during anaphase and G1, and is required for the degradation of cyclin B. CDCA3 is a cytosolic protein and a substrate of APC. It associates with Skp-1 and is required for the degradation of the cdk1 inhibitor wee1, a tyrosine kinase. Degradation of CDCA3 leads to an accumulation of wee1 during interphase []. The CDCA3 protein contains an F-box-like region and a KEN box; the latter is required for association with the APC complex.
