Effects of deletion of different PP2C protein phosphatase genes on stress responses in Saccharomyces cerevisiae.

A key mechanism of signal transduction in eukaryotes is reversible protein phosphorylation, mediated through protein kinases and protein phosphatases (PPases). Modulation of signal transduction by this means regulates many biological processes. Saccharomyces cerevisiae has 40 PPases, including seven protein phosphatase 2C (PP2C PPase) genes (PTC1-PTC7). However, their precise functions remain poorly understood. To elucidate their cellular functions and to identify those that are redundant, we constructed 127 strains with deletions of all possible combinations of the seven PP2C PPase genes. All 127 disruptants were viable under nutrient-rich conditions, demonstrating that none of the combinations induced synthetic lethality under these conditions. However, several combinations exhibited novel phenotypes, e.g. the Δptc5Δptc7 double disruptant and the Δptc2Δptc3Δptc5Δptc7 quadruple disruptant exhibited low (13°C) and high (37°C) temperature-sensitive growth, respectively. Interestingly, the septuple disruptant Δptc1Δptc2Δptc3Δptc4Δptc5Δptc6Δptc7 showed an essentially normal growth phenotype at 37°C. The Δptc2Δptc3Δptc5Δptc7 quadruple disruptant was sensitive to LiCl (0.4 m). Two double disruptants, Δptc1Δptc2 and Δptc1Δptc4, displayed slow growth and Δptc1Δptc2Δptc4 could not grow on medium containing 1.5 m NaCl. The Δptc1Δptc6 double disruptant showed increased sensitivity to caffeine, congo red and calcofluor white compared to each single deletion. Our observations indicate that S. cerevisiae PP2C PPases have a shared and important role in responses to environmental stresses. These disruptants also provide a means for exploring the molecular mechanisms of redundant PTC gene functions under defined conditions.

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