Heat stress
The heat shock response in bacteria is a protective mechanism to cope with heat-induced damage to proteins by synthesizing, a specific set of proteins known as heat shock proteins (HSPs) (Lindquist 1986; Schlesinger 1990). The heat shock response is mediated by the alternative sigma factor or 32. Under stress condi- tions an elevated environmental temperature causes a transient increase in a 32 transcription and transient stabilization of a 32 pro tein levels, which is normally unstable. The 12 directs tion of RNA polymerase (RNAP) from the heat shock promoters thus, results in the induction of HSPs. Most HSPs behave as molecular chaperones that function to bind to and stabilize nonnative polypeptides that are generated during protein synthesis or by heat denaturation of existing proteins, modulate folding pathways to misfolding or aggregation of proteins, and promote protein refolding and proper assembly los and Welch 1993). A number of molecular chaperones have been identified in E. coli, including Dnak (HSP70), Dna), GrpE GroEL (HSP60), and GroES and most of them are heat inducible (Gross 1996; Missiakas and others 1996a).