Suppressors of a Saccharomyces cerevisiae pkc1 mutation identify alleles of the phosphatase gene PTC1 and of a novel gene encoding a putative basic leucine zipper protein

Abstract

The PKC1 gene product, protein kinase C, regulates a mitogen-activated protein kinase (MAPK) cascade, which is implicated in cell wall metabolism. Previously, we identified the pkc1-4 allele in a screen for mutants with increased rates of recombination, indicating that PKC1 may also regulate DNA metabolism. The pkc1-4 allele also conferred a temperature-sensitive (ts) growth defect. Extragenic suppressors were isolated that suppress both the ts and hyperrecombination phenotypes conferred by the pkc1-4 mutation. Eight of these suppressors fell into two complementation groups, designated KCS1 and KCS2. KCS1 was cloned and found to encode a novel protein with homology to the basic leucine zipper family of transcription factors. KCS2 is allelic with PCT1, a previously identified type 2C serine/threonine protein phosphatase. Although mutation of either KCS1 or PTC1 causes little apparent of phenotype, the kcs1Δptc1Δ double mutant fails to grow at 30°. Furthermore, the ptc1 deletion mutation is synthetically lethal in combination with a mutation in MPK1, which encodes a MAPK homologue proposed to act in the PKC1 pathway. Because PTC1 was initially isolated as a component of the Hog1p MAPK pathway, it appears that these two MAPK cascades share a common regulatory feature.