The schizosaccharomyces pombe casein kinase II a and β subunits: Evolutionary conservation and positive role of the β subunit

Casein kinase II is a key regulatory enzyme involved in many cellular processes, including the control of growth and cell division. We report the molecular cloning and sequencing of cDNAs encoding the α and the β subunits of casein kinase II of Schizosaccharomyces pombe. The deduced amino acid sequence of Cka1, the α catalytic subunit, shows high sequence similarity to α subunits identified in other species. The amino acid sequence of Ckb1, the S. pombe β subunit, is 57% identical to that of the human β subunit. Cka1 overexpression results in no detectable phenotype. In contrast, Ckb1 overexpression inhibits cell growth and cytokinesis, with formation of multiseptated cells. Disruption of the ckb1⁺ gene causes a cold-sensitive phenotype and abnormalities in cell shape. In these cells, the casein kinase II activity is reduced to undetectable levels, demonstrating that Ckb1 is required for enzyme activity in vivo. In agreement with this, the activity measured in a strain expressing high levels of Cka1 is enhanced only when the Ckb1 protein is coexpressed. Altogether, our data suggest that Ckb1 is a positive regulator of the enzyme activity, and that it plays a role in mediating the interaction of casein kinase II with downstream targets and/or with additional regulators.