TEMPERATURE-SENSITIVE MUTATIONS OF THE CKA1 GENE REVEAL A ROLE FOR CASEIN KINASE-II IN MAINTENANCE OF CELL POLARITY IN SACCHAROMYCES-CEREVISIAE

Casein kinase II (CKII) of Saccharomyces cerevisiae contains two disti nct catalytic subunits, gamma and alpha', that are encoded by the CKA1 and -2 genes, respectively. We have constructed conditional alleles o f the CKA1 gene. In contrast to cka1 cka2(ts) strains, which exhibit a defect in both G(1) and G(2)/M cell cycle progression, cha1(ts) cha2 strains continue to divide for three cell cycles after a shift to rest rictive temperature and then arrest as a mixture of budded and unbudde d cells with a spherical morphology, Arrested cells exhibit continued growth, a nonpolarized actin cytoskeleton, delocalized chitin depositi on, and a significant fraction of multinucleate cell bodies, confirmin g the presence of a cell polarity defect in cha1(ts) strains, The pres ence of budded as well as unbudded cells in the arrested population su ggests that CKII is required for maintenance rather than establishment of cell polarity, although a role in both processes is also possible. The terminal phenotype of cha1(ts) strains bears a strong resemblance to that of orb5 strains of Schizosaccharomyces pombe, which carry a t emperature-sensitive CKII catalytic subunit mutation, but the underlyi ng mechanism appears to be different in the two cases, These results e stablish a requirement for CKII in cell polarity in S. cerevisiae and provide the first evidence for functional specialization of CKA1 and - 2.