Regulation of the Alternative Sigma Factor σ E during Initiation, Adaptation, and Shutoff of the Extracytoplasmic Heat Shock Response in Escherichia coli

Abstract

ABSTRACT The alternative sigma factor σ E is activated in response to stress in the extracytoplasmic compartment of Escherichia coli . Here we show that σ E activity increases upon initiation of the stress response by a shift to an elevated temperature (43°C) and remains at that level for the duration of the stress. When the stress is removed by a temperature downshift, σ E activity is strongly repressed and then slowly returns to levels seen in unstressed cells. We provide evidence that information about the state of the cell envelope is communicated to σ E primarily through the regulated proteolysis of the inner membrane anti-sigma factor RseA, as the degradation rate of RseA is correlated with the changes in σ E activity throughout the stress response. However, the relationship between σ E activity and the rate of degradation of RseA is complex, indicating that other factors may cooperate with RseA and serve to fine-tune the response.