Osmo-regulation of bacterial transcription via poised RNA polymerase.

Adaptation to high-salt environments is critical for the survival of a wide range of cells, especially for pathogenic bacteria that colonize the animal gut and urinary tract. The adaptation strategy involves production of the salt potassium glutamate, which induces a specific gene expression program that produces electro-neutral osmolytes while inhibiting general sigma(70) transcription. These data show that in Escherichia coli potassium glutamate stimulates transcription by disengaging inhibitory polymerase interactions at a sigma(38) promoter. These occur in an upstream region that is marked by an osmotic shock promoter DNA consensus sequence. The disruption activates a poised RNA polymerase to transcribe. This transcription program leads to the production of osmolytes that are shown to have only minor effects on transcription and therefore help to restore normal cell function. An osmotic shock gene expression cycle is discussed.