CLONING AND DISRUPTION OF CKB2, THE GENE ENCODING THE 32-KDA REGULATORY BETA'-SUBUNIT OF SACCHAROMYCES-CEREVISIAE CASEIN KINASE-II

Casein kinase II of Saccharomyces cerevisiae is composed of two distin ct catalytic subunits, alpha and alpha', and two distinct regulatory s ubunits, beta and beta' (Padmanabha, R. and Glover, C. V. C. (1987) J. Biol. Chem. 262, 1829-1835; Bidwai, A. P., Reed, J. C., and Glover, C . V. C. (1994) Arch. Biochem. Biophys. 309, 348-355). We report here t he cloning, sequencing, and disruption of the CKB2 gene encoding the b eta'-subunit. The deduced amino acid sequence of Ckb2 displays only 40 -45% identity to other beta-subunit sequences reported to date, allowi ng a better definition of conserved features of this protein. Most not able is the conservation of a cysteine containing sequence, CPX(3)C-X( 22)-CPXC, which may constitute a novel metal-binding motif. The degree of sequence divergence of Ckb2 is comparable to that of the Drosophil a Stellate protein, a testis-specific protein of unknown function, sug gesting that the latter may function as a second beta-subunit in Droso phila. CKB2 is located on the right arm of chromosome XV between the H IR2 and WHI2 loci and has not been previously identified genetically. Haploid and homozygous diploid cells harboring a ckb2 null allele are viable, demonstrating that the beta'-subunit does not have an essentia l function distinct from that of beta. Strains lacking a functional CK B2 gene appear to grow normally on both fermentable and non-fermentabl e carbon sources, mate and sporulate normally, and display normal resi stance to nitrogen starvation and heat shock. However, haploid strains harboring disruptions of both the beta' gene and either of the cataly tic subunit genes exhibit a synthetic phenotype consisting of slow gro wth and flocculation in rich glucose medium. The occurrence of this sy nthetic phenotype implies that the beta'-subunit interacts physically and/or functionally with both the alpha- and alpha'-subunits in vivo.