General Stress Response

Induction of the general stress response by one stress affords significant cross-protection against other stresses. Activation of σB initiates the primary and secondary events that collectively bring about the general stress response. The diverse stresses which elicit σB activity fall into two classes: (i) energy stresses, such as those caused by carbon, phosphorus, or oxygen starvation, or by the addition of oxidative micouplers to the growth medium; and (ii) environmental stresses, such as acid, ethanol, heat, or salt stress. Site-directed mutagenesis has shown that the Per-Arnt-Sim (PAS) domain of RsbP, and at least one defining residue within the domain, are indeed important for the energy stress response. In contrast, the kinase activity of RsbT is essential for the environmental stress response, suggesting that modulation of this activity is one route by which signals enter the branch. In contrast, the RsbU, RsbP, and SpoIIE phosphatases each contain one or two additional domains that regulate phosphatase activity in response to diverse inputs, and this appears to be an emerging theme in stress-signaling PP2C phosphatases in both prokaryotic and eukaryotic organisms. Interestingly, components of the partner-switching mechanism appear to be widely distributed among the eubacteria. In some cases, such as in Synechocystis sp. strain PCC 6803, all components of the switch are present and manifest the predicted activities in vitro. In other cases, such as the E. coli RsbV ortholog YrbB, no obvious partner exists in the genome.