PROTEIN PHOSPHATASE 2C, ENCODED BY PTC1(-SHOCK RESPONSE OF SCHIZOSACCHAROMYCES-POMBE(), IS IMPORTANT IN THE HEAT)

Protein phosphatase 2C (PP2C), an Mg2+-dependent enzyme that dephospho rylates serine and threonine residues, defines one of the three major families of structurally unrelated eukaryotic protein phosphatases. Me mbers of the two other families of protein phosphatases are known to h ave important cellular roles, but very little is known about the biolo gical functions of PP2C. In this report we describe a genetic investig ation of a PP2C enzyme in the fission yeast Schizosaccharomyces pombe. We discovered ptc1(+) (phosphatase two C) as a multicopy suppressor g ene of swo1-26, a temperature-sensitive mutation of a gene encoding th e heat shock protein hsp90. The ptc1(+) gene product is a 40-kDa prote in with similar to 24% identity to a rat PP2C protein. Purified Ptc1 h as Mg2+-dependent casein phosphatase activity, confirming that it is a PP2C enzyme. A ptc1 deletion mutant is viable and has approximately n ormal levels of PP2C activity, observations consistent with the fact t hat ptc1(+) is a member of a multigene family. Although a ptc1 deletio n mutant is viable, it has a greatly reduced ability to survive brief exposure to elevated temperature. Moreover, ptc1(+) mRNA levels increa se 5- to 10-fold during heat shock. These data, demonstrating that Ptc 1 activity is important for survival of heat shock, provide one of the first genetic clues as to the biological functions of PP2C.