SCK1, A HIGH COPY NUMBER SUPPRESSOR OF DEFECTS IN THE CAMP-DEPENDENT PROTEIN-KINASE PATHWAY IN FISSION YEAST, ENCODES A PROTEIN HOMOLOGOUS TO THE SACCHAROMYCES-CEREVISIAE SCH9 KINASE

Schizosaccharomyces pombe regulates intracellular cAMP levels, and thu s cAMP-dependent protein kinase (PKA) activity, in response to changes in nutrient conditions. Mutations in any of eight git genes inhibit g lucose repression off fbp1 transcription, alter the cell morphology, a nd cause a reduction in the growth rate. The eight git genes encode co mponents of an adenylate cyclase activation pathway, adenylate cyclase itself, and the catalytic subunit of PKA. Three of these genes have b een identified in other studies as regulators of meiosis. Here we show that the sck1 gene, cloned as a high copy number suppressor of a muta tion in git3, is able to suppress the defects conferred by a mutation in any of these git genes. Sequence analysis suggests that sck1 encode s a protein most closely related to the Saccharomyces cerevisiae SCH9 protein kinase that had previously been identified as a high copy numb er suppressor of mutations in S. cerevisiae that reduce or eliminate P KA activity. Disruption of the sck1 gene causes a significant delay in exit from stationary phase when combined with a disruption of the pka 1 (git6) gene encoding the catalytic subunit of PKA. However, the sck1 disruption by itself has little or no effect upon fbp1 transcription, meiosis, or exit from stationary phase, and does not enhance the cons titutive fbp1 transcription observed in a pka1 mutant. Therefore, sck1 appears to function in a redundant fashion to pka1, but to varying de grees, in the pathways regulated by pka1.