Abstract
Cell cycle progression is driven by cyclin-dependent kinases (CDKs). Activation of CDKs requires interaction with cyclins, and phosphorylation of the specific residues within the T-loops by CDK-activating kinases(CAKs). CAKs also phosphorylate the carboxy terminal domain (CTD) of the largest subunit of RNA polymerase II. The Arabidopsis genome encodes four potential CAKs (CDKD;1, CDKD;2, CDKD;3, CDKF;1). The plant-specific CDKF;1 phosphorylates CDKD;2 and CDKD;3, which then phosphorylate CTD and CDK, respectively. Recently, we isolated T-DNA insertion mutants of CAKs. The mutant of CDKF;1, which has a high CDK-phosphorylation activity, was embryonic lethal, whereas that of CDKD;3 grew up normally. These results suggest that the CDK-phosphorylation activity derived by CDKF;1 may be enough to activate CDKs in plant cells. We are currently analyzing different CAK complexes present in plant cells in terms of enzyme activity and subunit composition.
