General stress response signalling: unwrapping transcription complexes by DNA relaxation via the sigma38 C-terminal domain.

Escherichia coli responds to stress by a combination of specific and general transcription signalling pathways. The general pathways typically require the master stress regulator sigma38 (rpoS). Here we show that the signalling from multiple stresses that relax DNA is processed by a non-conserved eight-amino-acid tail of the sigma 38 C-terminal domain. By contrast, responses to two stresses that accumulate potassium glutamate do not rely on this short tail, but still require the overall C-terminal domain. In vitro transcription and footprinting studies suggest that multiple stresses can target a poised RNA polymerase and activate it by unwrapping DNA from a nucleosome-like state, allowing the RNA polymerase to escape into productive mode. This transition can be accomplished by either the DNA relaxation or potassium glutamate accumulation that characterizes many stresses.