Acquired thermotolerance following heat shock protein synthesis prevents impairment of mitochondrial ATPase activity at elevated temperatures in Saccharomyces cerevisiae (original) (raw)
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Journal of General Microbiology, 1990
The pmal.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. pmal.1 mutants exhibited higher resistance to ethanol and osmotic stress, but lower tolerance to ultraviolet damage, as compared to wild-type cells. pmal.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, pmal.1 lowered subsequent tolerances of much higher lethal temperatures. Analysis of pulse-labelled S. cerevisiae proteins revealed reduced heat-shock protein synthesis in the pmal.1 mutant after a 25-38 "C heat shock. This may explain the greater increases in thermotolerance in wild-type as compared to pmal.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 pmal.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.
Microbiology
The role of membrane integrity and the membrane ATPase in the mechanism of thermotolerance in Saccharomyces cerevisiae was investigated. The resistance to lethal heat of a mutant strain with reduced expression of the membrane ATPase was significantly less than that of the wild-type parent. However, prior exposure to sub-lethal temperatures resulted in the induction of similar levels of thermotolerance in the mutant compared to the parent strain, suggesting that the mechanism of sub-lethal heat-induced thermotolerance is independent of ATPase activity. Supporting this, exposure to sub-lethal heat stress did not result in increased levels of glucose-induced acid efflux at lethal temperatures and there was little correlation between levels of acid efflux and levels of heat resistance. ATPase activity in crude membrane preparations from sub-lethally heat-stressed cells was similar to that in preparations from unstressed cells. Study of net acid flux during heating revealed that pre-stressed cells were able to protect the proton gradient for longer. This may confer an 'advantage' to these cells that results in increased thermotolerance. This was supported by the observation that prior exposure to sub-lethal heat resulted in a transient protection against the large increase in membrane permeability that occurs a t lethal temperatures. However, no protection against the large drop in intracellular pH was detected. Sub-lethal heat-induced protection of membrane integrity also occurred to the same extent in the reduced-expression membrane ATPase mutant, further implying that the mechanism of induced thermotolerance is independent of ATPase activity. T o conclude, although the membrane ATPase is essential for basal heat resistance, thermotolerance induced by prior exposure to stress is largely conferred by a mechanism that is independent of the enzyme.
Russian Journal of Genetics, 2004
Heat shock protein Hsp104 of Saccharomyces cerevisiae functions as a protector of cells against heat stress. When yeast are grown in media containing nonfermentable carbon sources, the constitutive level of this protein increases, which suggests an association between the expression of Hsp104 and yeast energy metabolism. In this work, it is shown that distortions in the function of mitochondria appearing as a result of mutation petite or after exposure of cells to the mitochondrial inhibitor sodium azide reduce the induction of Hsp104 synthesis during heat shock. Since the addition of sodium azide suppressed the formation of induced thermotolerance in the parent type and in mutant hsp104,the expression of gene HSP104 and other stress genes during heat shock is apparently regulated by mitochondria.
The Journal of cell biology, 1996
SSH1, a newly identified member of the heat shock protein (hsp70) multigene family of the budding yeast Saccharomyces cerevisiae, encodes a protein localized to the mitochondrial matrix. Deletion of the SSH1 gene results in extremely slow growth at 23 degrees C or 30 degrees C, but nearly wild-type growth at 37 degrees C. The matrix of the mitochondria contains another hsp70, Ssc1, which is essential for growth and required for translocation of proteins into mitochondria. Unlike SSC1 mutants, an SSH1 mutant showed no detectable defects in import of several proteins from the cytosol to the matrix compared to wild type. Increased expression of Ssc1 partially suppressed the cold-sensitive growth defect of the SSH1 mutant, suggesting that when present in increased amounts, Ssc1 can at least partially carry out the normal functions of Ssh1. Spontaneous suppressors of the cold-sensitive phenotype of an SSH1 null mutant were obtained at a high frequency at 23 degrees C, and were all found ...
Responses ofSaccharomyces cerevisiae to thermal stress
Biotechnology and Bioengineering, 2005
We studied the mechanisms involved in heat gradient-induced thermotolerance of Saccharomyces cerevisiae. Yeasts were slowly heated in a nutrient medium from 25 to 508C at 0.58C/min or immediately heat shocked at 508C, and both sets of cultures were maintained at this temperature for 1 h. Cells that had been slowly heated showed a 50-fold higher survival rate than the rapidly heated cells. Such thermotolerance was found not to be related to protein synthesis. Indeed Hsp104 a known protein involved in yeast thermal resistance induced by a preconditioning mild heat treatment, was not synthesized and cycloheximide addition, a protein synthesis inhibitor, did not affect the thermoprotective effect. Moreover, a rapid cooling from 50 to 258C applied immediately after the heat slope treatment inhibited the mechanisms involved in thermotolerance. Such observations lead us to conclude that heat gradient-induced thermal resistance is not directly linked to mechanisms involving intracellular molecules synthesis or activity such as proteins (Hsps, enzymes) or osmolytes (trehalose). Other factors such as plasma membrane phospholipid denaturation could be involved in this phenomenon.
Heat Shock–Induced Changes in the Respiration of the Yeast Saccharomyces cerevisiae
Microbiology, 2001
The incubation of Saccharomyces cerevisiaeat elevated temperature (45°C) stimulated the respiration of yeast cells and decreased their survival rate. The respiration-deficient mutant of this yeast was found to be more tolerant to the elevated temperature than the wild-type strain. At the same time, the cultivation of the wild-type strain in an ethanol-containing medium enhanced the respiration, catalase activity, and thermotolerance of yeast cells, as compared with their growth in a glucose-containing medium. It is suggested that the enhanced respiration of yeast cells at 45°C leads to an intense accumulation of reactive oxygen species, which may be one of the reasons for the heat shock–induced cell death.