A PP2C phosphatase containing a PAS domain is required to convey signals of energy stress to the σ(B) transcription factor of Bacillus subtilis

Abstract

The σ(B) transcription factor of the bacterium Bacillus subtilis is activated by growth-limiting energy or environmental challenge to direct the synthesis of more than 100 general stress proteins. Although the signal transduction pathway that conveys these stress signals to σ(B) is becoming increasingly well understood, how environmental or energy stress signals enter this pathway remains unknown. We show here that two PP2C serine phosphatases - RsbP, which is required for response to energy stress, and RsbU, which is required for response to environmental stress - each converge on the RsbV regulator of σ(B). According to the current understanding of σ(B) regulation, in unstressed cells the phosphorylated RsbV anti-anti-σ is unable to complex the RsbW anti-σ, which is then free to bind and inactivate σ(B). We can now advance the model that either PP2C phosphatase, when triggered by its particular class of stress, can remove the phosphate from RsbV and thereby activate σ(B). The action of the previously described RsbU is known to be controlled by dedicated upstream signalling components that are activated by environmental stress. The action of the RsbP phosphatase described here requires an energy stress, which we suggest is sensed, at least in part, by the PAS domain in the amino-terminal region of the RsbP phosphatase. In other bacterial signalling proteins, similar PAS domains and their associated chromophores directly sense changes in intracellular redox potential to control the activity of a linked output domain.