Which sigma factor is involved in heat shock response in E. coli?
Thermal stress induces accumulation unfolded proteins triggering activation alternate sigma factor σ32 encoded by rpoH gene, also known as heat shock sigma. Under normal growth, DnaK chaperone sequesters σ32 targeting FtsH proteolysis maintaining low levels. Upon heat shock, misfolded proteins titrate chaperones freeing σ32 to associate with core polymerase redirecting holoenzyme to promoters of heat shock regulon including groEL, dnaK, clpB chaperones and proteases. Promoters possess distinct consensus recognized preferentially by σ32. Therefore σ32 specifically orchestrates heat shock response, contrasting housekeeping σ70, σ54 nitrogen response, σ28 flagellar synthesis.
Ref: Alberts Molecular Biology Cell Chapter 7: Sigma32 heat shock response E coli RpoH regulation; Watson Chapter 14 Alternative sigma factors stress