[Induction of Hsp104 synthesis in Saccharomyces cerevisiae is inhibited by the petite mutation in the stationary growth phase].

The elevation of Hsp104 (heat shock protein) content under heat shock plays a key role in yeast (Saccharomyces cerevisiae) cells. Hsp104 synthesis is increased under heat stress in the stationary growth phase. As shown, the loss of mitochondrial DNA (petite mutation) inhibited the induction of the Hsp104 synthesis under heat stress (39 degrees C) during the transition to the stationary growth phase. Also, the petite mutation suppressed the activity of antioxidant enzymes in the same phase, which led to lower thermotolerance. At the same time, the mutation inhibited production of the reactive oxygen species and prevented cell death under heat shock in the logarithmic growth phase. The results of this study suggest that disruption of the mitochondrial functional state suppresses the expression level of yeast nuclear genes upon transitioning to the stationary growth phase.

Mechanism of Saccharomyces cerevisiae yeast cell death induced by heat shock. Effect of cycloheximide on thermotolerance.

The mechanism of yeast cell death induced by heat shock was found to be dependent on the intensity of heat exposure. Moderate (45°C) heat shock strongly increased the generation of reactive oxygen species (ROS) and cell death. Pretreatment with cycloheximide (at 30°C) suppressed cell death, but produced no effect on ROS production. The protective effect was absent if cycloheximide was added immediately before heat exposure and the cells were incubated with the drug during the heat treatment and recovery period. The rate of ROS production and protective effect of cycloheximide on viability were significantly decreased in the case of severe (50°C) heat shock. Treatment with cycloheximide at 39°C inhibited the induction of Hsp104 synthesis and suppressed the development of induced thermotolerance to severe shock (50°C), but it had no effect on induced thermotolerance to moderate (45°C) heat shock. At the same time, Hsp104 effectively protected cells from death independently of the intensity of heat exposure. These data indicate that moderate heat shock induced programmed cell death in the yeast cells, and cycloheximide suppressed this process by inhibiting general synthesis of proteins.

Effect of amiodarone on thermotolerance and Hsp104p synthesis in the yeast Saccharomyces cerevisiae.

Amiodarone (AMD) is known to induce a transient increase in cytosolic Ca2+ level in cells of the yeast Saccharomyces cerevisiae. In the present study the effect of AMD on the thermotolerance and Hsp104p synthesis of the yeast was studied. AMD induced Hsp104p synthesis and increased survival of the yeast after a severe heat shock (50°C). The development of thermotolerance to a considerable extent depended on the presence of Hsp104p. The same effect was achieved by treatment with the classical uncoupler CCCP, which is also known to increase the cytosolic Ca2+ level. It is supposed that the change in intracellular Ca2+ concentration plays an important role in activation of the HSP104 gene expression and in increasing the thermotolerance of the yeast. The possible link between mitochondrial activity and calcium homeostasis is discussed.

[Induction of synthesis of Hsp104 of Saccharomyces cerevisiae in heat shock is controlled by mitochondria]. / Induktsiia sinteza Hsp104 Saccharomyces cerevisiae pri teplovom shoke nakhoditsia pod kontrolem mitokhondrii.

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 effect of sodium malonate on yeast thermotolerance]. / Deistvie malonata natriia na termotolerantnost' drozhzhei.

The study of the effect of malonate (an inhibitor of the succinate dehydrogenase complex of the respiratory chain of mitochondria) on the thermotolerance of the fermentative Saccharomyces cerevisiae and nonfermentative Rhodotorula rubra yeasts showed that malonate augmented the damaging effect of heat shock on the yeasts utilizing glucose (or other sugars) by means of oxidative phosphorylation. At the same time, malonate did not influence and sometimes even improved the thermotolerance of the yeasts utilizing glucose through fermentation. The suggestion is made that cell tolerance to heat shock depends on the normal functioning of mitochondria. On the other hand, their increased activity at elevated temperatures may accelerate the formation of cytotoxic reactive oxygen species and, hence, is not beneficial to cells.

[The absence of direct relationship between the ability of yeasts to grow at elevated temperatures and their survival after lethal heat shock]. / Otsutstvie priamoi zavisimosti mezhdu sposobnost'iu drozhzhei rasti pri povyshenii temperatury i ikh vyzhivaemost'iu posle letal'nogo teplovogo shoka.

The study of the growth of the yeasts Rhodotorula rubra, Saccharomyces cerevisiae, and Debaryomyces vanriji at elevated temperatures and their survival after transient lethal heat shock showed that the ability of these yeasts to grow at supraoptimal temperatures (i.e., their thermoresistance) and their ability to tolerate lethal heat shocks (i.e., their thermotolerance) are determined by different mechanisms. The thermotolerance of the yeasts is suggested to be mainly determined by the division rate of cells before their exposure to heat shock.

[Effect of cytochrome oxidase inhibitors on the yeast thermotolerance]. / Deistvie ingibitorov tsitokhromoksidaznogo kompleksa na termoustoichivost' drozhzhei.

The investigation of the effect of the cytochrome oxidase inhibitors sodium cyanide and sodium azide on the thermotolerance of the yeasts Rhodotorula rubra, Debaryomyces vanriji, and Saccharomyces cerevisiae showed that these inhibitors diminish the thermotolerance of R. rubra and D. vanriji, but do not affect the thermotolerance of S. cerevisiae. Taking into account the fact that, unlike the latter yeast, R. rubra and D. vanriji are nonfermentative yeasts, the difference in the effects of the inhibitors on the yeast thermotolerance can be readily explained by the different types of glucose utilization (either oxidative or fermentative) in these yeasts. The data obtained also provide evidence that there is a correlation between the functional activity of mitochondria and the thermotolerance of yeast cells.

[The effect of sodium azide on the thermotolerance of the yeast Saccharomyces cerevisiae and Candida albicans]. / Izuchenie deistviia azida natriia na termoustoichivost' drozhzhei Saccharomyces cerevisiae i Candida albicans.

The addition of sodium azide (a mitochondrial inhibitor) at a concentration of 0.15 mM to glucosegrown Saccharomyces cerevisiae or Candida albicans cells before exposing them to heat shock increased cell survival. At higher concentrations of azide, its protective effect on glucose-grown cells decreased. Furthermore, azide, even at low concentrations, diminished the thermotolerance of galactose-grown yeast cells. It is suggested that azide exerts a protective effect on the thermotolerance of yeast cells when their energy requirements are met by the fermentation of glucose. However, when cells obtain energy through respiratory metabolism, the azide inhibition of mitochondria enhances damage inflicted on the cells by heat shock.

[Heat shock-induced changes in the respiration of the yeast Saccharomyces cerevisiae]. / Izmenenie dykhaniia pri deistvii teplovogo shoka na drozhzhi Saccharomyces cerevisiae.

The incubation of Saccharomyces cerevisiae at elevated temperature (45 degrees 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 degrees C leads to an intense accumulation of reactive oxygen species, which may be one of the reasons for the heat shock-induced cell death.

[Effect of sodium azide on heat-shock resistance in Saccharomyces cerevisiae and Debaryomyces vanriji yeasts]. / Vliianie azida natriia na ustoichivost' k teplovomu shoku drozhzhei Sacharomyces cerevisiae i Debaryomyces vanriji.

The pretreatment of Saccharomyces cerevisiae and Debaryomyces vanriji with sodium azide was found to induce thermotolerance in both yeasts, whereas sodium azide used in combination with heat shock enhanced the thermotolerance of S. cerevisiae and substantially decreased the thermotolerance of D. vanriji. It is suggested that the different responses of the yeasts to sodium azide during heat shock are due to the different functional organizations of their mitochondrial apparatus.

Association of bacteria and yeasts in hot springs.

The thermophilic bacterium Bacillus sp. strain TB-1 was isolated in association with the yeast Debaryomyces vanriji from hot springs at 46 degrees C. It was shown that TB-1 excreted thiamine into the culture broth, which not only promoted D. vanriji growth in mixed culture but also increased the maximal temperature for yeast growth.

Formation of the enzymatic apparatus of respiration in growing cells. Communication II. Reorganization of the respiratory cycle of mitochondria in the corn root tip.

The content of cytochromes a,b and c, the activity of marker enzymes of the matrix and inner membrane of the mitochondria: glutamate dehydrogenase and cytochrome oxidase, as well as the rate of absorption of O2 by root segments in the presence of respiratory substrates, oxygen, inhibitors of respiration, and dinitrophenol, were determined. The intensification of cell respiration in the phase of elongation is determined not so much by new formation of cytochrome components of the respiratory cycle (during this period there is an accumulation only of cytochrome c) as by reorganization of the respiratory cycle (primarily its portion NADH - cytochrome b) and synthesis of enzymes of the matrix.