The eukaryotic cell cycle is controlled by cyclin-dependent kinases (CDKs). Plants possess six types of CDK, among which the B-type CDK (CDKB) is expressed specifically from the late S- to the M-phase. We demonstrate that the expression of Arabidopsis CDKB2 is under the control of the protein degradation machinery. beta-Glucuronidase fused to a putative PEST motif of CDKB2 was unstable in tobacco Bright Yellow-2 cells and Arabidopsis plants, and its degradation was arrested by the proteasome inhibitor MG132. We propose that the abundance of CDKB2 protein is regulated not only at the transcriptional level, but also through proteasome-mediated protein degradation.