Abstract
Signaling pathways regulating cell cycle progression ultimately converge on the control of activity of cyclin-dependent kinases (CDKs). Activation of CDKs is controlled by phosphorylation, as well as by binding to cyclins. Phospholylation of threonine residue within the T-loop of CDK is catalyzed by a CDK-activating kinase (CAK). Four Arabidopsis CAKs (CAK1At-CAK4At) have been identified and we found that CAK1At phosphorylates and activates CAK2At, CAK4At and human CDK2 in vitro. In contrast, CDK activities are inhibited by phosphorylation of threonine and tyrosine residues by Wee1 kinase. Recently we have revealed that Wee1 of Arabidopsis phosphorylates CDKs and inactivates not only but also CAKs. We shall report gene expression, subcellular localization, protein acclimation and enzyme activity of each kinase by using synchronized Arabidopsis suspension cultures. Furthermore, we shall present some data on a response to cytokinins.
