PLASMA-MEMBRANE ATPASE ACTION AFFECTS SEVERAL STRESS TOLERANCES OF SACCHAROMYCES-CEREVISIAE AND SCHIZOSACCHAROMYCES-POMBE AS WELL AS THE EXTENT AND DURATION OF THE HEAT-SHOCK RESPONSE

The pma1.1 mutations of Saccharomyces cerevisiae and Schizosaccharomyces pombe decrease plasma-membrane ATPase activity. This study investigated how they affect different stress tolerances, and the extent and duration of the heat-shock response. pma1.1 mutants exhibited higher resistance to ethanol and osmotic stress, but lower tolerance to ultraviolet damage, as compared to wild-type cells. pma1.1 mutations also increased tolerance of the lethal temperature of 48°C in cells in which no heat-shock response had been induced. However, after induction of a heat-shock response and elevated thermotolerance by a 25-38°C upshift, then maintaining cells at 38°C for 40 min, pma1.1 lowered subsequent tolerances of much higher lethal temperatures. Analysis of pulse-labelled S. cerevisiae proteins revealed reduced heat-shock protein synthesis in the pma1.1 mutant after a 25-38°C heat shock. This may explain the greater increases in thermotolerance in wild-type as compared to pma1.1 cells after both were given identical 25-38°C shocks. With more severe treatment (25-42°C), heat-shock protein synthesis in wild-type cells, although initially high, was switched off more rapidly than in the pma1.1 mutant. These results indicate that plasma-membrane ATPase action exerts a major influence over several stress tolerances, as well as the extent and duration of heat-shock protein synthesis following induction of the heat-shock response.