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PubMed2002

Ty1 defect in proteolysis at high temperature.

Retrotransposition of the Ty1 element of Saccharomyces cerevisiae is temperature sensitive. Transposition activity of Ty1 is abolished at temperatures above 34 degrees C. In this report, we show that the major block to transposition at high temperature is the inhibition of processing of the Gag-Pol-p199 polyprotein and the concomitant reduction of reverse transcriptase (RT) activity. Expression of a Ty1 protease construct in Escherichia coli shows that protease enzymatic activity is inherently temperature sensitive. In yeast, Gag processing is only partially inhibited at high temperature, while cleavage of the Gag-Pol polyprotein is completely inhibited. Sites of proteolytic processing are differentially susceptible to cleavage during growth at high temperature. Overall levels of the Gag-Pol polyprotein are reduced at high temperature, although the efficiency of the requisite +1 frameshifting event appears to be increased. RT activity is inherently relatively temperature resistant, yet no cDNA is made at high temperature and the amount of RT activity is greatly reduced in virus-like particles formed at high temperature. Taken together, these results suggest that alterations in Ty1 proteins that occur at high temperature affect both protease activity and RT activity, such that Ty1 transposition is abolished.

DNA, Complementary↗
PubMed1996

Heat-shock treatment reduces in situ temperature in yeast at sub-lethal high temperature.

Cells from the yeast Schizosaccharomyces pombe IFO-0342, once heat shocked and then treated with ultra-centrifugation showed a significant increase in tolerance compared to non heat-shocked control cells as estimated by colony forming unit (CFU). Fluorescence microscopical observation of these treated cells when stained with DAPI revealed that in non heat-shocked cells the chromatin regions were dislocated to one end due to the acceleration force of gravity. However, prior heat-shocked cells or 2.0 M glycerol suspended cells showed normal localization. From these results, it has been postulated that the interior part of the heat-shocked cells becomes viscous, and that in situ the temperature of the cell interior part might be reduced under semi-lethal high temperature.

Hot Temperature↗
PubMed2005

Thermal ablation and high-temperature thermal therapy: overview of technology and clinical implementation.

High-temperature hyperthermia or thermal therapy is being applied for destruction of cancerous tissue, eradication or reduction of benign tumours and targeted tissue modification and remodelling. Many of these high-temperature technologies provide a minimally-invasive alternative with lower morbidities compared to the traditional surgical procedures. The effects of high-temperature thermal exposure on tissues, examples of heating technology and procedures of clinical practice related to high-temperature thermal therapy are reviewed. This brief review encompasses interstitial, endocavity, intraluminal and external applications of RF, microwave, ultrasound, laser and thermal conduction energy sources. The technology is prevalent and in various levels of advancement, with the move toward more spatially-accurate and controllable heating systems combined with image-guidance and treatment verification warranted, especially for the treatment of cancer.

Hot Temperature↗
PubMed2003

Measurement of As, P, and S in the waste gases and water emitted from semiconductor processes by high-temperature hydrogen reduction gas chromatography.

A quick, sensitive, and accurate method, high-temperature hydrogen reduction gas chromatography (GC) (1,2), for measuring arsenic (As), phosphorus (P), and sulfur (S) in the waste gases and water emitted from semiconductor processes is proposed in this paper. A high-temperature hydrogen reduction system that changes As, P, S, and their compounds into hydrides by atomic hydrogen has been designed. It is convenient to detect these elements in solid, liquid, and gaseous samples by high-temperature hydrogen reduction GC without pretreating samples. The lower detection limits of As, P, and S by this method are 0.01, 0.003, 0.02 mg/L, respectively, and the values of relative standard deviation are 6.2%, 8.6%, and 0.3%, respectively. Results determined by high-temperature hydrogen reduction GC are primarily accordant to those by conventional methods such as colorimetry and ion chromatography. The error statistics of this analysis method also show that high-temperature hydrogen reduction GC can be successfully used to determine trace As, P, and S in waste gases and wastewater emitted from semiconductor processes.

Journal Article↗
PubMed1978

The temperature sensitive mutant 72c. II. Accumulation at high temperature of ppGpp and pppGpp in the presence of protein synthesis.

A heat sensitive mutant of E. coli has been analyzed. A shift to restrictive temperature leads to an accumulation of ppGpp and pppGpp in both the parental and the mutant strains (both are relA+). The pool of these compounds is shown to decrease with time after the temperature shift in the case of the parental strain, but remains at the same elevated level in the case of the mutant. The temperature shift of the mutant leads to an apparent reduction of stable RNA synthesis; this inhibition can be released by chloroamphenicol or tetracycline. Gross protein synthesis is more or less unaffected at restrictive temperature. In the parental strain little effect is seen on RNA and protein synthesis after the temperature shift. A relA derivative of the mutant does not show the same inhibition of RNA synthesis at high temperature. Sedimentation analysis suggests that mutant 70S ribosome are more stable, when exposed to a lowered Mg2+ concentration, than are 70S ribosomes from the parental strain. In addition, the relative amounts of the two forms of ribosomal protein S6, which can be obtained on DEAE chromatography (Held et al., 1973), are significantly changed in the mutant.

Bacterial Proteins↗
PubMed2001

Role of trehalose in growth at high temperature of Salmonella enterica serovar Typhimurium.

Moderate osmolality can stimulate bacterial growth at temperatures near the upper limit for growth. We investigated the mechanism by which high osmolality enhances the thermotolerance of Salmonella enterica serovar Typhimurium, by isolating bacteriophage MudI1734-induced insertion mutations that blocked the growth-stimulatory effect of 0.2 M NaCl at 45 degrees C. One of these mutations proved to be in the seqA gene (a regulator of initiation of DNA synthesis). Because this gene is cotranscribed with pgm (which encodes phosphoglucomutase), it is likely to be polar on the expression of the pgm gene. Pgm catalyzes the conversion of glucose-6-phosphate to glucose-1-phosphate during growth on glucose, and therefore loss of Pgm results in a deficiency in a variety of cellular constituents derived from glucose-1-phosphate, including trehalose. To test the possibility that the growth defect of the seqA::MudI1734 mutant at high temperature in medium of high osmolality is due to the block in trehalose synthesis, we determined the effect of an otsA mutation, which inactivates the first step of the trehalose biosynthetic pathway. The otsA mutation caused a growth defect at 45 degrees C in minimal medium containing 0.2 M NaCl that was similar to that caused by the pgm mutation, but otsA did not affect growth rate in this medium at 37 degrees C. These results suggest that the growth defect of the seqA-pgm mutant at high temperature could be a consequence of the block in trehalose synthesis. We found that, in addition to the well-known osmotic control, there is a temperature-dependent control of trehalose synthesis such that, in medium containing 0.2 M NaCl, cells grown at 45 degrees C had a fivefold higher trehalose pool size than cells grown at 30 degrees C. Our observations that trehalose accumulation is thermoregulated and that mutations that block trehalose synthesis cause a growth defect at high temperature in media of high osmolality suggested that this disaccharide is crucial for growth at high temperature either for turgor maintenance or for protein stabilization.

Bacterial Outer Membrane Proteins↗
PubMed2006

Use of DNA marker to select well-adapted Phaseolus-symbionts strains under acid conditions and high temperature.

Soil acidity and high temperature contribute to the failure of nodulation in the common bean. It is therefore urgent to select strains with a high competitive ability under these stress conditions. Two Egyptian Rhizobium etli strains, EBRI 2 and EBRI 26, were examined against Rhizobium tropici CIAT 899G labeled with the gus (beta-glucuronidase) reporter gene. EBRI 2 and EBRI 26 were less competitive than CIAT 899G under acid conditions with both the Egyptian cultivar Giza 3 and the Colombian cultivar Rab 39. However, EBRI 2 and EBRI 26 gave higher nodule occupancy (78% and 62.5, respectively) than the nodule occupancy (18.5% and 35%) obtained by CIAT 899G at 35 degrees C with cultivar Giza 3. Soil acidity (pH 5.8) was less detrimental to the nodule occupancy of EBRI 2 than EBRI 26 when they tested in competition with CIAT 899G.

DNA, Plant↗
PubMed2005

[Effects of high temperature on grain filling and some physiological characteristic in flag leaves of hybrid rice].

The effects of high temperature on grain filling rate and some physiological indexes in flag leaves in hybrid rice Teyou 559 were studied. The results showed that chlorophyll content and superoxide dismutase (SOD) activity in flag leaves were lower significantly by high temperature stress (Figs.2A and 3A). The electrolyte leakage and malondialdehyde (MDA) content were higher significantly under high temperature stress (Figs.2B and 3B). The proline (Pro), ascorbic acid (AsA), glutathione (GSH), soluble protein and soluble sugar contents were lower significantly by high temperature stress than those of the control (Figs.4,5 and 6). Both the rate of grain filling and grain dry matter accumulation become lower significantly under high temperature stress (Figs.7 and 8). Therefore, it was suggested that high temperature accelerated the senescence of rice leaf and decreased the photosynthesis rate during grain filling period, and then which was the main reason in physiology which resulted the decrease of grain filling rate, seed setting rate, grain weight and yield.

Ascorbic Acid↗
PubMed1990

Raman spectroscopic studies of hen egg-white lysozyme at high temperatures and pressures.

In situ high-temperature, high-pressure Raman experiments on 3 mM (pH 5) aqueous solutions of hen egg-white (HEW) lysozyme show a decrease in the relative height of the 505 cm-1 band associated with S-S stretching vibrations at 72 degrees C (1 bar). The peak height changes are accompanied by significant band broadening, and the integrated band intensity does not change within experimental error. The effect of increased pressure at 72 degrees C was to hinder broadening of the 505 cm-1 band. HEW lysozyme (2.4 mM, pH 5) was also heated at 76 degrees C, 80 degrees C, and 95 degrees C for different periods of time, and aliquots were quenched to room temperature for Raman and enzymatic activity measurements. After 9 hr at 76 degrees C, the protein exhibits enzyme activity less than 50% of the initial value, and approximately 50% reduction in activity is achieved after 3 hr at 80 degrees C or 1 hr at 95 degrees C. The Raman results suggest that different irreversibly denatured conformations are attained during prolonged exposures at these different temperatures. It is apparent from these studies that the S-S stretch intensity is decreased irreversibly.

Amino Acid Sequence↗
PubMed2000

Advances in the physics of high-temperature superconductivity

The high-temperature copper oxide superconductors are of fundamental and enduring interest. They not only manifest superconducting transition temperatures inconceivable 15 years ago, but also exhibit many other properties apparently incompatible with conventional metal physics. The materials expand our notions of what is possible, and compel us to develop new experimental techniques and theoretical concepts. This article provides a perspective on recent developments and their implications for our understanding of interacting electrons in metals.

Journal Article↗
PubMed1980

Inhibition of ethylene production by 2,4-dinitrophenol and high temperature.

2,4-Dinitrophenol (DNP) and high temperature (35 to 40 C) are known to inhibit C(2)H(4) production in various plant tissues. The present study was made to determine the step in the C(2)H(4) biosynthetic pathway (methionine --> S-adenosylmethionine [SAM] --> 1-aminocyclopropane-1-carboxylic acid [ACC] --> C(2)H(4)) at which these treatments exert their inhibitory effect. In mung bean hypocotyls the dose-inhibition curves for the effect of DNP on auxin-dependent C(2)H(4) production (in which auxin exerts its effect by stimulating the conversion of SAM to ACC) and on ACC-dependent C(2)H(4) production (in which ACC is directly utilized as precursor) were similar. It was concluded, therefore, that DNP at low concentrations (below 50 micromolar) exerted its effect primarily on the conversion of ACC to C(2)H(4), a step which is common to both systems. This view was further substantiated by quantitative analysis of the intermediates in the biosynthetic sequence. DNP exerted little influence on the content of SAM but caused a significant increase in the ACC content and marked inhibition in C(2)H(4) production, indicating that the conversion of ACC to C(2)H(4) is the crossover point. At higher concentrations (above 100 micromolar), DNP inhibited the conversion of methionine to ACC and to C(2)H(4), and this effect could be attributed to the inhibition of SAM synthesis.The optimal temperature for maximal C(2)H(4) production by apple tissue and mung bean hypocotyl is about 30 C. An increase in temperature to 35 C caused an accumulation of endogenous ACC, whereas C(2)H(4) production was greatly reduced. These results suggest that the conversion of ACC to C(2)H(4) is highly vulnerable to high temperature inhibition.

Journal Article↗