FIG. 6.
Model for the σE cell envelope stress response. Expression of the gene encoding σE (sigE) is regulated at the level of transcription by the CseB/CseC two-component signal transduction system. In response to signals originating in the cell envelope when it is under stress, the sensor kinase, CseC, becomes autophosphorylated and transfers this phosphate to the response regulator, CseB. Phospho-CseB activates the promoter of the sigE operon, and σE is recruited by core RNA polymerase to transcribe genes with cell envelope-related functions. Note that >90% transcription from the sigE promoter terminates just downstream of sigE and that the sigE promoter itself is not a σE target (28). CseA is a lipoprotein localized to the extracytoplasmic face of the cell membrane, and loss of CseA results in upregulation of the sigE promoter. CseA might interact directly with the sensor domain of CseC, or, alternatively, loss of CseA might lead to destabilization of the cell envelope, which in turn leads to induction of the CseBC signal transduction system.