CLONING AND DISRUPTION OF CKB1, THE GENE ENCODING THE 38-KDA BETA-SUBUNIT OF SACCHAROMYCES-CEREVISIAE CASEIN KINASE-II (CKII) - DELETION OFCKII REGULATORY SUBUNITS ELICITS A SALT-SENSITIVE PHENOTYPE

Saccharomyces cerevisiae casein kinase II (CKII) contains two distinct catalytic (alpha and alpha') and regulatory (beta and beta') subunits , We report here the isolation and disruption of the gene, CKB1, encod ing the 38-kDa beta subunit. The predicted Ckb1 sequence includes the N-terminal autophosphorylation site, internal acidic domain, and poten tial metal binding motif (CPX(3)C-X(22)-CPXC) present in other beta su bunits but is unique in that it contains two additional autophosphoryl ation sites as well as a 30-amino-acid acidic insert. CKB1 is located on the left arm of chromosome VII, approximately 33 kilobases from the centromere and does not correspond to any previously characterized ge netic locus. Haploid and diploid strains lacking either or both beta s ubunit genes are viable, demonstrating that the regulatory subunit of CKII is dispensable in S. cerevisiae. Such strains exhibit wild type b ehavior with regard to growth on both fermentable and nonfermentable c arbon sources, mating, sporulation, spore germination, and resistance to heatshock and nitrogen starvation, but are salt sensitive. Salt sen sitivity is specific for NaCl and LiCl and is not observed with KCI or agents which increase osmotic pressure alone, These data suggest a ro le for CKII in ion homeostasis in S. cerevisiae.