Heat shock control element

The enhanced expression of metal-induced stress proteins is controlled primarily at the transcriptional level similar to the induction of hsps by heat (Wu et al. 1986). Regulation of hsp genes in eukaryotic systems is mediated by a cw-acting heat shock control element (HSE) that is found in multiple copies upstream of the transcriptional start site (Pelham 1982). Transcriptional activation of the hsp genes is mediated by a ran -acting protein, known as the heat shock factor (HSF), which binds specifically to the HSE (Wu 1984a,b). 

Induction of heat-shock proteins depends upon a heat-shock promoter element (HSE) that binds an activating transcription factor HSF.452-455 An increase in temperature not only induces synthesis of heat-shock proteins but represses synthesis of most other proteins. Thus, in E. coli or Salmonella a shift from 30°C to 42°C causes the appearance of 13 heat-shock proteins. At 50°C synthesis of almost all other proteins stops. In E. coli transcription of heat-shock genes is controlled by alternative factors, o32 and oE.456 456a... 

Fig. 4.4. The principle of signal transduction by nuclear receptors. Nuclear receptors are ligand-controlled transcription factors that bind cognate DNA sequences, or hormone responsive elements (HRE). The hormone acts as a regulating ligand. Most nuclear receptors bind their cognate HREs, which tend to be symmetrically organized, as homo- or heterodimers. The DNA-bound, activated receptor stimulates transcription initiation via direct or indirect protein-protein interactions with the transcription initiation complex. The arrows demonstrate the different possible configurations of the HRE (see also 4.6). H hormone Hsp heat shock protein.

Cellular control of HSP expression All HSPs are regulated by a small family of transcription factors called heat shock factor (HSFl ). During a stress condition, HSFl and 2 are hyperphosphorylated in a ras-dependent manner by MAP kinases. Binding of these active HSFl factors to DNA sequences called heat shock elements in the promoters of all stress-inducible genes occurs. This leads to increased transcription of HSP genes and induction of HSP proteins. 

Some transcription control mechanisms can be categorized based on a common response to certain metabolic factors. Enhancers that respond to these factors are called response elements. Examples include the heat-shock element (HSE), the glucocorticoid-response element (GRE), the metal-response element (MRE), and the cyclic-AMP-response element (GRE). 

Transcription Regulation in Eukaryotes The heat-shock element responds to increased temperature. The metal-response element responds to the presence of heavy metals, such as cadmium, and the cyclic-AMP-response element controls a wide variety of genes based on cAMP levels in the cell. 

The deceptively simple stoichiometry and the importance of the elements concerned led to much early investigation of the chain reaction between hydrogen and oxygen, mostly in static systems at moderate temperatures. Unfortunately the main kinetic features of the reaction under these conditions are controlled by heterogenous steps occurring at the walls of the reaction vessel it is not possible to observe the separation of the kinetics into zones of initiation, exponential growth of chain centres, and heat release by recombination. However this reaction has been extensively investigated in the shock tube by Dr... 

If the container itself does not include a heating element, any immersion heater should be insulated to avoid the potential of electrical shock and should include a cut-out device if the temperature exceeds the set point. Alternatively, a second temperature sensor should be placed in the heat bath to act as a circuit breaker to cut off power to the heater if its thermostat fails. The thermostat clearly should always be set well below the flash point of the heating liquid in use. A thermometer placed in the bath at all times it is in use is recommended to provide a visual indication of the actual temperature of the bath. Digital controllers normally provide this additional information. 

Oil baths used for heating vessels should utilize oils that do not smoke, such as silicone oil. They are heated with heating elements that can be bought commercially or sometimes they are heated with a laboratory-made heating element that is controlled by a variable transformer. There are several potential hazards from these burns from touching hot surfaces or splatters of hot oil, potential for fires if the flash point of the oil is exceeded, and potential for electrical shock from unguarded terminals (especially with lab-made oil baths). 

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