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PubMed1972

Activation heat, activation metabolism and tension-related heat in frog semitendinosus muscles.

1. Frog semitendinosus muscles were stretched to various lengths beyond the rest length (l(0)) and their initial heat and isometric tension production were measured.2. As the overlap between the thick and thin filaments is reduced, the initial twitch heat and tension decline in a linear manner. At a point at which the twitch tension approaches zero, the initial heat is 30% of that seen at l(0). It is concluded that this heat is the activation heat and reflects the energetics of calcium release and reaccumulation. The initial heat at shorter sarcomere lengths appears to be the sum of the activation heat plus a heat production associated with the interaction of the thick and thin filaments.3. A similar relationship between heat and tension production is seen in tetanic contractions.4. The time course of activation heat production in a twitch can be resolved into two phases: a temperature insensitive (Q(10) < 1.3) ;fast' phase (with a time constant of 45 msec) and a temperature sensitive (Q(10) = 2.8) ;slow' phase (with a time constant of 330 msec at 0 degrees C).5. Measurements of the creatine phosphate (PC) hydrolysis by muscles contracting isometrically at various muscle lengths at and beyond l(0), indicate an enthalpy change of -11.2 kcal/mole PC hydrolysed. The enthalpy change for the ATP hydrolysis by muscles stretched so that little or no tension was produced with stimulation was -9.9 kcal/mole ATP hydrolysed. It is concluded that the net activation heat is produced by the hydrolysis of PC or ATP.

Adenosine Triphosphate↗
PubMed1991

Temperature regulation during acute heat loads in rats after short-term heat exposure.

Eleven rats were kept at an ambient temperature of 33.5 degrees C (HC) for 4-5 consecutive days, 9 additional rats were subjected to 33.5 degrees C for approximately 5 h daily (HI) for the same period, and 12 controls (Cn) were kept at 24 degrees C. After the exposure, the rats were placed in a direct calorimeter, where the wall temperature was set at 24 degrees C, and subjected to direct internal heating (6.2 W.kg-1, 30 min) through an intraperitoneal electric heater. After the first heat load and when thermal equilibrium had been attained again, the rats were subjected to indirect external warming by raising the jacket water temperature surrounding the calorimeter from 24.0 to 38.8 degrees C in 90 min. Hypothalamic (Thy) and colonic temperatures (Tco), evaporative and nonevaporative heat loss, and metabolic heat production (M) before the acute heat loads did not differ among the groups. During heat loads, the latent times for the onsets of the rises in tail skin temperature and evaporation were significantly longer, and Thy and Tco at the start of increases in heat losses tended to be higher, in the HC than in the Cn. M significantly decreased in all groups, but the magnitude and duration of reduction in M were significantly greater in the HC than in the Cn. There were no differences between the thermoregulatory responses to heat loads of the HI and Cn. These results suggest that in HC the threshold core temperature for heat loss response and the upper critical temperature have already shifted to a higher level and that HC respond to heat stress more strongly with the reduction of M than Cn. Short-term intermittent heat exposure had little effect on the thermoregulatory mechanisms in rats.

Acclimatization↗
PubMed2000

Heat storage in horses during submaximal exercise before and after humid heat acclimation.

The effect of humid heat acclimation on thermoregulatory responses to humid and dry exercise-heat stress was studied in six exercise-trained Thoroughbred horses. Horses were heat acclimated by performing moderate-intensity exercise for 21 days in heat and humidity (HH) [34.2-35.7 degrees C; 84-86% relative humidity (RH); wet bulb globe temperature (WBGT) index approximately 32 degrees C]. Horses completed exercise tests at 50% of peak O(2) uptake until a pulmonary arterial temperature (T(pa)) of 41.5 degrees C was attained in cool dry (CD) (20-21.5 degrees C; 45-50% RH; WBGT approximately 16 degrees C), hot dry (HD 0) [32-34 degrees C room temperature (RT); 45-55% RH; WBGT approximately 25 degrees C], and HH conditions (HH 0), and during the second hour of HH on days 3, 7, 14, and 21, and in HD on the 18th day (HD 18) of heat acclimation. The ratios of required evaporative capacity to maximal evaporative capacity of the environment (E(req)/E(max)) for CD, HD, and HH were approximately 1.2, 1.6, and 2.5, respectively. Preexercise T(pa) and rectal temperature were approximately 0.5 degrees C lower (P < 0. 05) on days 7, 14, and 21 compared with day 0. With exercise in HH, there was no effect of heat acclimation on the rate of rise in T(pa) (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in T(pa) was significantly slower, and rate of heat storage was decreased on HD 18 compared with HD 0. It was concluded that, during uncompensable heat stress in horses, heat acclimation provided modest heat strain advantages when E(req)/E(max) was approximately 1.6, but at higher E(req)/E(max) no advantages were observed.

Acclimatization↗
PubMed1987

Heat potentiation of radiation damage versus radiation potentiation of heat damage.

The enhanced lethality of mammalian cells after combined treatment with hyperthermia and radiation is usually attributed to heat potentiation of radiation damage. However, it has been suggested that the situation may be reversed and that radiation may act as a modifier for heat damage. To test this hypothesis, BP-8 murine sarcoma cells were subjected to sequential radiation and heat treatments and the kinetics and extent of cell death were evaluated with the [125I]-iododeoxyuridine prelabeling assay. Cell death after heating was rapid and essentially complete within 2 days after heat exposure, whereas radiation death was slow and became apparent only after a delay period of 3 days. Combined exposure of cells to radiation and heat caused a pronounced increase in the delayed component of cell death, that is, the radiation component of death. Irradiation of cells before heating did not change the early heat component of cell death even in cells that were exposed to massive radiation doses of up to 300 Gy prior to heating. These results indicate that the increased cell death observed in hyperthermia/radiation-treated cells results from heat potentiation of radiation damage, not radiation potentiation of heat damage.

Animals↗
PubMed1995

Shivering and rewarming after cardiac surgery: comparison of ventilator circuits with humidifier and heated wires to heat and moisture exchangers.

BACKGROUND: Detrimental physiologic effects of shivering in the cardiac surgery patient have been well documented. Rewarming techniques have been compared, with noted differences in the incidence of shivering. Ventilator circuits have not been examined independently from other rewarming variables. OBJECTIVE: To compare heated wire humidification circuits with heat and moisture exchanger circuits on the incidence of shivering and speed and pattern of rewarming in mechanically ventilated patients. METHODS: A prospective, descriptive, correlational study was done on 140 adult cardiac surgery patients in a university teaching medical center. All subjects underwent cardiac surgical procedures with hypothermic cardiopulmonary bypass. Subjects were randomized to humidified, heated wire circuits (n = 70) or heat and moisture exchanger circuits (n = 70). Heated water blankets were used on all patients. RESULTS: Mean intensive care unit admission temperature was 35.28 degrees C. No statistical differences were found in preoperative, demographic, or operative course data between treatment and control groups. Shivering was more common in the heat and moisture exchanger group than in the heated wire group. In our analysis, the only variable associated with shivering was the type of ventilator circuit. Patients using heated wire systems rewarmed more rapidly and had significantly higher temperatures than did patients using heat and moisture exchangers. CONCLUSION: These data suggest that use of heated wire humidified ventilator circuits with heated water blankets in adult cardiac surgery patients significantly reduces the incidence of shivering and results in a more rapid return to normothermia.

Aged↗
PubMed1999

Higher induction of heat shock protein 72 by heat stress in cisplatin-resistant than in cisplatin-sensitive cancer cells.

Induction of the heat shock proteins (HSPs) is involved in the increased resistance to cancer therapies such as chemotherapy and hyperthermia. We used two human ovarian cancer cell lines; a cisplatin (CDDP)-sensitive line A2780 and its CDDP-resistant derivative, A2780CP. The concentration of intracellular glutathione (GSH) is higher (2.7-fold increase) in A2780CP cells than in A2780 cells. A mild treatment with a heat stress (42 degrees C for 30 min) induced synthesis of both the heat shock protein 72 (Hsp72) mRNA and the HSP72 protein in A2780CP cells, but not in A2780 cells. In contrast, a severe heat stress (45 degrees C for 30 min) increased synthesis of the HSP72 protein in the two cell lines. The induced level of the HSP72 protein by the severe treatment was higher in A2780CP than in A2780 cells. The gel mobility shift assay showed that DNA binding activities of the heat shock factor (HSF) in the two cell lines were induced similarly and significantly by the mild heat stress. Immunocytochemistry using an anti HSF1 antibody also indicated that mild heat stress activated the HSF1 translocation from the cytosol to the nucleus similarly in the both cell lines. Pretreatment of CDDP-sensitive A2780 cells with N-acetyl-L-cysteine, a precursor of GSH, effectively enhanced induction of the Hsp72 mRNA by the mild heat stress. The present findings demonstrate that induction of the Hsp72 mRNA by the mild heat stress was more extensive in CDDP-resistant A2780CP cells. It is likely that the higher GSH concentration in A2780CP cells plays an important role in promoting Hsp72 gene expression induced by the mild heat stress probably through processes downstream of activation of HSF-DNA binding.

Cisplatin↗
PubMed1995

Salicylate triggers heat shock factor differently than heat.

Sodium salicylate has the unusual property of partially inducing the human heat shock response (Jurivich, D. A., Sistonen, L., Kroes, R., and Morimoto, R. I. (1992) Science 255, 1243-1245). Salicylate induces the DNA binding state of the human heat shock transcription factor (HSF), but this is insufficient to elevate heat shock gene expression. Because it is not known how HSF enhances heat shock gene expression, further analysis of the transcriptionally inert, salicylate-induced HSF was undertaken to potentially identify components of the heat shock response that are necessary for full transcriptional induction. Like thermal stress, exposure of HeLa cells to salicylate led to the induction of HSF1 into a DNA-bound state. Despite continued exposure of cells to salicylate, HSF1.DNA binding attenuated much more rapidly than a continuous heat shock. Western blot analysis revealed that the salicylate-induced form of HSF1 was not hyperphosphorylated like the heat-induced form. Furthermore, supershifts of the HSF1 bound to an heat shock element (HSE) oligonucleotide by monoclonal antibodies to phosphoamino acids revealed that salicylate induced threonine phosphorylation of HSF1, whereas heat led to a predominance of HSF1 serine phosphorylation. These data suggest that salicylate-independent signals are necessary to convert HSF1 into a transactivator of heat shock gene expression and that brief acquisition of DNA binding by this factor is insufficient to maximally enhance transcription.

Blotting, Western↗
PubMed2003

Activation of heat shock genes is not necessary for protection by heat shock transcription factor 1 against cell death due to a single exposure to high temperatures.

Heat shock response, which is characterized by the induction of a set of heat shock proteins, is essential for induced thermotolerance and is regulated by heat shock transcription factors (HSFs). Curiously, HSF1 is essential for heat shock response in mammals, whereas in avian HSF3, an avian-specific factor is required for the burst activation of heat shock genes. Amino acid sequences of chicken HSF1 are highly conserved with human HSF1, but those of HSF3 diverge significantly. Here, we demonstrated that chicken HSF1 lost the ability to activate heat shock genes through the amino-terminal domain containing an alanine-rich sequence and a DNA-binding domain. Surprisingly, chicken and human HSF1 but not HSF3 possess a novel function that protects against a single exposure to mild heat shock, which is not mediated through the activation of heat shock genes. Overexpression of HSF1 mutants that could not bind to DNA did not restore the susceptibility to cell death in HSF1-null cells, suggesting that the new protective role of HSF1 is mediated through regulation of unknown target genes other than heat shock genes. These results uncover a novel role of vertebrate HSF1, which has been masked under the roles of heat shock proteins.

Adenoviridae↗
PubMed2000

Heat induced expression of CD95 and its correlation with the activation of apoptosis upon heat shock in rat histiocytic tumor cells.

The heat shock response is a universal phenomenon and is among the most highly conserved cellular responses. However, BC-8, a rat histiocytoma, fails to mount a heat shock response unlike all other eukaryotic cells. In the absence of induction of heat shock proteins, apoptotic cell death is activated in BC-8 tumor cells upon heat shock. We demonstrate here that stable transformants of BC-8 tumor cells transfected with hsp70 cDNA constitutively express hsp70 protein and are transiently protected from heat induced apoptosis for 6-8 h. In addition heat stress induces CD95 gene expression in these tumor cells. There is a delay in CD95 expression in hsp70 transfected cells suggesting a correlation between the cell surface expression of CD95 and the time of induction of apoptosis in this tumor cell line. Also expression of CD95 antigen appears to inhibit the interaction between heat shock factors and heat shock elements in these cells resulting in the lack of heat shock response.

Animals↗
PubMed1999

Inhibition of heat shock factor activity prevents heat shock potentiation of glucocorticoid receptor-mediated gene expression.

Using mouse L929 cells stably transfected with a glucocorticoid receptor (GR)-responsive murine mammary tumor virus-chloramphenicol acetyltransferase (MMTV-CAT) reporter gene (LMCAT2 cells), we have shown that cellular stress (heat or chemical shock) can cause a dramatic increase in the levels of dexamethasone (Dex)-induced CAT gene expression. We refer to this response as the heat shock potentiation effect, or HSPE. As the cellular heat shock response also involves the activation of heat shock transcription factor (HSF), we have, in the present study, examined the role of HSF in the stress potentiation of GR by use of a flavonoid compound, quercetin, recently shown to selectively inhibit the stress response in a variety of human and murine cell lines. Analysis of the HSPE, as well as heat shock protein synthesis and activation of HSF during time-courses of recovery following heat shock, revealed a similar pattern for each response, with peak activities occurring about 16 h after stress. These data suggest a correlation between the activation of both GR and HSF in stressed cells. In L929 cells stably transfected with a CAT reporter plasmid under the control of the HSF-responsive hsp70 promoter (LHSECAT cells), pretreatment with quercetin was found to cause a dose- and time-dependent inactivation of HSF activity following heat shock, but only when added before the stress event. In LMCAT2 cells, quercetin similarly inhibited both heat and chemical shock potentiation of Dex-induced GR activity. This activity of quercetin was not the result of post-transcriptional or general cytotoxic properties, as quercetin (1) did not significantly affect GR or HSF activities when added after the stress event, (2) did not reduce CAT gene expression as controlled by the constitutive SV40 early promoter, and (3) did not alter normal (non-stress), Dex-induced MMTV-CAT expression. Thus, quercetin appears to be an effective and selective inhibitor of HSF stress-induced activation and its ability to prevent the stress potentiation of GR suggests either a direct or indirect involvement by stress-activated HSF in this process, or the existence of a regulatory step common to both the heat shock and HSPE responses.

Animals↗
PubMed1988

Thermotolerance and heat shock protein induction by slow rates of heating.

The magnitude of thermotolerance and the level of heat shock protein (HSP) expression have been measured in Chinese hamster ovary cells after gradual temperature transients from 37 degrees or 39 degrees to 42 degrees or 43 degrees C. When the level of thermotolerance was measured by clonogenic survival after challenging temperatures between 42 degrees and 43 degrees, substantial thermotolerance was observed. However, when the challenging temperature was raised to 45 degrees C, proportionally less thermotolerance was apparent. Heat shock proteins were quantitated by scanning densitometry of radiographs and, in the case of HSP 70, by immunoassay. Scanning densitometry revealed that low levels of heat shock proteins were synthesized during the heating gradients, but less than after a heat shock at 45 degrees C that delivered an equivalent heat dose. The immunoassay of HSP 70 levels measures both pre-existing and newly synthesized protein, and showed that there was net increase in HSP 70 during two of the heating gradients tested, despite the increase in synthesis noted on the gels. Higher turnover of HSP 70 at the elevated temperatures possibly accounted for the failure to detect a net gain in total protein. In contrast, the total amount of HSP 70 doubled during the 6 hr following a heat shock of 45 degrees for 10 min, an equivalent heat dose to one of the gradients where no net increase in HSP 70 was measured by immunoassay. It appears, then, that tolerance to hyperthemia at 43 degrees C or below may occur under some conditions in the absence of elevated levels of HSP 70, but tolerance to higher temperatures is more closely correlated with increased levels of heat shock proteins. However, even at higher temperatures, our data show disparities between the levels of HSP measured and the thermotolerance expressed.

Animals↗
PubMed1995

Cordycepin blocks recovery of non-heat-shock mRNA translation following heat shock in Drosophila.

Treatment of cells with cordycepin (3-deoxyadenosine), an inhibitor of cytoplasmic adenylation, blocks the restoration of normal translation following heat shock. Cordycepin also reduces heat-shock protein 70 (Hsp70) protein synthesis greater than 10-fold, while having little to no effect on mRNA accumulation. Parallel analysis of the poly(A)-binding protein detects no change in its abundance during heat shock or subsequent recovery. These results suggest that normal, non-heat-shock mRNA translational repression during heat shock may be caused by deadenylation, and that readenylation is required for restoration of activity. However, three independent analyses of the adenylation status of mRNAs during heat shock and recovery indicate that no significant changes in polyadenylation occur. (a) The total poly(A) content decreases by only about 10% during heat shock; (b) the size of the poly(A) tract decreases only marginally, from an average length of 75-90 nucleotides in non-heated cells to 45-60 nucleotides during heat shock; (c) virtually all mRNAs bind to oligo d(T)-cellulose, whether extracted from normal-temperature, heat-shock or recovered cells. Our results are most consistent with a model where the process of readenylation, rather than the specific poly(A) tail length, influences translational activation during recovery, paralleling a proposed model for the activation of translation during Xenopus oocyte maturation.

Animals↗
PubMed1998

Conventional and novel PKC isoenzymes modify the heat-induced stress response but are not activated by heat shock.

In mammalian cells, the heat-induced stress response is mediated by the constitutively expressed heat shock transcription factor 1 (HSF1). Upon exposure to elevated temperatures, HSF1 undergoes several post-translational modifications, including inducible phosphorylation or hyperphosphorylation. To date, neither the role of HSF1 hyperphosphorylation in regulation of the transcriptional activity of HSF1 nor the signaling pathways involved have been characterized. We have previously shown that the protein kinase C (PKC) activator, 12-O-tetradecanoylphorbol 13-acetate (TPA), markedly enhances the heat-induced stress response, and in the present study we elucidate the mechanism by which PKC activation affects the heat shock response in human cells. Our results show that several conventional and novel PKC isoenzymes are activated during the TPA-mediated enhancement of the heat shock response and that the enhancement can be inhibited by the specific PKC inhibitor bisindolylmaleimide I. Furthermore, the potentiating effect of TPA on the heat-induced stress response requires an intact heat shock element in the hsp70 promoter, indicating that PKC-responsive pathways are able to modulate the activity of HSF1. We also demonstrate that PKC is not activated by heat stress per se. These results reveal that PKC exhibits a significant modulatory role of the heat-induced stress response, but is not directly involved in regulation of the heat shock response.

Carcinogens↗
PubMed2004

Heat illness in athletes: the dangerous combination of heat, humidity and exercise.

In 1980, 1700 people died during a prolonged heat wave in a region under-prepared for heat illness prevention. Dramatically underreported, heat-related pathology contributes to significant morbidity as well as occasional mortality in athletic, elderly, paediatric and disabled populations. Among US high school athletes, heat illness is the third leading cause of death. Significant risk factors for heat illness include dehydration, hot and humid climate, obesity, low physical fitness, lack of acclimatisation, previous history of heat stroke, sleep deprivation, medications (especially diuretics or antidepressants), sweat gland dysfunction, and upper respiratory or gastrointestinal illness. Many of these risk factors can be addressed with education and awareness of patients at risk. Dehydration, with fluid loss occasionally as high as 6-10% of bodyweight, appears to be one of the most common risk factors for heat illness in patients exercising in the heat. Core body temperature has been shown to rise an additional 0.15-0.2 degrees C for every 1% of bodyweight lost to dehydration during exercise. Identifying athletes at risk, limiting environmental exposure, and monitoring closely for signs and symptoms are all important components of preventing heat illness. However, monitoring hydration status and early intervention may be the most important factors in preventing severe heat illness.

Adaptation, Physiological↗
PubMed2002

Whole-blood concentrations of glutathione in cattle exposed to heat stress or a combination of heat stress and endophyte-infected tall fescue toxins in controlled environmental conditions.

OBJECTIVE: To determine whether cattle exposed to heat stress alone or heat stress while consuming endophyte-infected fescue (EIF) have lower whole-blood (WB) concentrations of glutathione (GSH). ANIMALS: 10 Simmental cows. PROCEDURE: Cows were sequentially exposed to thermoneutral (TN; 2 weeks; 18 C, 50% relative humidity [RH]), heat stress (HS; 2 weeks; alternating 4-hour intervals at 26 and 33 C; 50% RH), and heat stress while consuming EIF (10 microg of ergovaline/kg/d; 2 weeks, HS + EIF). Blood samples were collected after each period and tested for GSH and oxidized glutathione (GSSG) concentrations. RESULTS: Feed consumption was similar when data were analyzed for time points at which WB concentrations of GSH or GSSG were determined. However, significant effects of treatment, cow, days exposed to heat, cow-by-treatment interaction, and treatment-by-days exposed to heat interaction were detected when data were considered simultaneously. Mean +/- SD hematocrit for TN, HS, and HS + EIF were 35.3+/-3, 33.3+/-2, and 37.1+/-3%, respectively. Mean WBGSH concentrations for TN, HS, and HS + EIF were 3.2+/-0.65, 2.7+/-0.62, and 2.4+/-0.56 mmol/L of RBC, respectively. Reduced WBGSH concentrations were associated with reduced feed intake during the later part of each heat period. CONCLUSIONS AND CLINICAL RELEVANCE: Decreased GSH and increased GSSG concentrations were evident during heat stress, especially when cattle consumed EIF These were associated with reduced feed intake during heat stress. Heat stress, reductions in feed intake, and thermoregulatory effects of EIF may induce oxidative stress in cattle.

Animals↗
PubMedDate not supplied

Heat sensitivity of bleomycin-sensitive CHO derivatives is not due to improper initialization of heat shock response.

We have investigated whether differences in the heat shock response exist between CHO and three bleomycin-sensitive, heat-sensitive CHO derivatives. The binding of heat shock factor (HSF) in response to heat and varying concentrations of bleomycin in the four cell lines was examined using a gel shift assay and a synthetic heat shock element (HSE). Heat (45 degrees C, 10 min) and exposure to 1 micrograms/ml bleomycin for 1 h at 37 degrees C induced similar levels of HSF binding in all four cell lines. We also examined if bleomycin dose and the length of recovery from bleomycin treatment affected the induction of HSF binding. The level of activated HSF binding to HSE was higher in cells treated with low doses (1 ng/ml) of bleomycin than in cells treated with 1 or 25 micrograms/ml bleomycin. The amount of activated HSF was directly proportional to the time elapsed since bleomycin treatment. Our results therefore indicate no difference between CHO and its bleomycin-sensitive derivatives in the ability to initiate the heat shock response as determined by the production of activated HSF in response to either heat or bleomycin. We conclude that the intrinsic thermosensitivity of these cell lines is not related to the early response to heat shock, but either occurs later in the pathway or is unrelated to events after heating.

Animals↗
PubMed1988

Heat intolerance, heat exhaustion monitored: a case report.

A 32-year-old male (Mr. A.), monitored during an 8-d heat acclimation (HA) investigation, unexpectedly exhibited heat intolerance and heat exhaustion. Thirteen other males completed HA without indications of either heat intolerance or heat exhaustion. Because Mr. A. responded normally to HA on days 1-4, the intervention of an unknown host factor on days 5-8 was suggested. Mr. A.'s heat exhaustion episode (day 8) was apparently forewarned by loss of body weight and increased delta HR, delta Tsk (days 5-8) and delta Tre (days 7-8) during daily 90-min trials. His symptoms indicated classical salt depletion heat exhaustion, but the calculated salt deficit (less than 0.1 g NaCl.kg-1 body weight) was mild. Post-heat exhaustion serum enzyme levels were either normal (ALT, AST) or acutely elevated (CPK). Blood beta-endorphin and cortisol levels were six times and two times greater than control values, respectively. This case report is unique because clinical/physiological measurements and blood analyses were performed before, during, and after heat intolerance and heat exhaustion.

Acclimatization↗
PubMed1990

DnaK, DnaJ, and GrpE heat shock proteins negatively regulate heat shock gene expression by controlling the synthesis and stability of sigma 32.

The Escherichia coli DnaK heat shock protein has been identified previously as a negative regulator of E. coli heat shock gene expression. We report that two other heat shock proteins, DnaJ and GrpE, are also involved in the negative regulation of heat shock gene expression. Strains carrying defective dnaK, dnaJ, or grpE alleles have enhanced synthesis of heat shock proteins at low temperature and fail to shut off the heat shock response after shift to high temperature. These regulatory defects are due to the loss of normal control over the synthesis and stability of sigma 32, the alternate RNA polymerase sigma-factor required for heat shock gene expression. We conclude that DnaK, DnaJ, and GrpE regulate the concentration of sigma 32. We suggest that the synthesis of heat shock proteins is controlled by a homeostatic mechanism linking the function of heat shock proteins to the concentration of sigma 32.

Alleles↗