Cell-cycle modulation of CK2 activity in tobacco BY-2 cells

Protein kinase CK2 is an ubiquitous Ser/Thr kinase essential for cell growt h. We have used the highly synchronizable tobacco BY-2 cell line to investi gate whether CK2 activity and expression are regulated in a cell cycle phas e-dependent manner in higher plants. Specific cDNA probes for tobacco CK2 a lpha and beta subunits, respectively, and polyclonal antibodies recognising alpha and beta subunits separately, were obtained to determine mRNA and pr otein levels of both subunits. Our results show that CK2 activity oscillate s throughout the cell cycle, peaking at G1/S and M phases, due to a posttra nslational regulation of the tetrameric enzyme. Additional levels of contro l of CK2 expression operate in relation to the proliferative state of the c ells, including differential accumulation of alpha and beta transcripts and posttranscriptional regulation of protein levels (beta subunit). Moreover, in vivo inhibition of CK2 activity corroborates the requirement of the fun ctional CK2 to progress through the cell division cycle, and suggests that CK2 might play an important role at the G2/M checkpoint.