The heat shock response of E. coli is regulated by changes in the concentration of σ32

Cells subjected to a heat shock, or a variety of other stresses,increase the synthesis of a set of proteins, known as heat shockproteins1–3. This response is apparently universal, occurring in the entire range from bacterial to mammalian cells. In Escherichia coli heat shock protein synthesis transiently increases following a shift from 30 °C to 42 °C as a result of changes in transcription initiation at heat shock promoters4–6. Heat shock promoters are recognized by RNA polymerase containing a sigma factor of relative molecular mass (Mr) 32,000 (32K) Eσ32 (refs 7, 8) and not Eσ70, the major form of RNA polymerase holoenzyme6. To determine whether changes in the concentration of σ32 regulate this response, we measured the amount of σ32 before and after shift to high temperature and found that it increased transiently during heat shock as a result of changes in σ32 synthesis and stability. Our results indicate that σ32 is directly responsible for regulation of the heat shock response.

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