Cloning and Disruption of CKB1, the Gene Encoding the 38-kDa β Subunit of Saccharomyces cerevisiae Casein Kinase II (CKII)

Saccharomyces cerevisiae casein kinase II (CKII) contains two distinct catalytic (a and a') and regulatory (/3 and /3') subunits. We report here the isolation and disruption of the gene, CKBl, encoding the 38-kDa /3 subunit. The predicted Ckbl sequence includes the N-terminal autophosphorylation site, internal acidic domain, and potential metal binding motif (CPXaC-~2-CPXC) present in other /3 subunits but is unique in that it contains two additional autophosphorylation sites as well as a 30-amino-acid acidic insert. CKBI is located on the left arm of chromosome VII, approximately 33 kilobases from the centromere and does not correspond to any previously characterized genetic locus. Haploid and diploid strains lacking either or both /3 subunit genes are viable, demonstrating that the regulatory subunit of CKII is dispensable in S. cerevisiae. Such strains exhibit wild type behavior with regard to growth on both fermentable and nonfermentable carbon sources, mating, sporulation, spore germination, and resistance to heatshock and nitrogen starvation, but are salt-sensitive. Salt sensitivity is specific for NaCI and LiCI and is not observed with KCI or agents which increase osmotic pressure alone. These data suggest a role for CKII in ion homeostasis in S. cereoisiae, Casein kinase II (CKIl)l is a messenger-independent Ser-Thr protein kinase which is ubiquitous among eukaryotes The CKII holoenzyme is a constitutively active ex 2 {32 heterotetramer composed of catalytic (ex) and regulatory ({3) subunits. Two distinct ex subunits encoded by separate genes are present in most organisms, although only a single ex subunit isoform has so far been identified in Drosophila melanogaster (Glover et al., 1983), Caenorhabditis elegans (Hu and Rubin, 1990a), and Schizosaccharomyces pombe Saccharomyces cerevisiae A second {3-like polypeptide, the product of the Stellate locus, has been identified in D. melanogaster