Figure 5.

(a) The GSR signaling pathway in Alphaproteobacteria is activated by environmental signals and integrates features of two-component and sigma factor–dependent regulation of gene expression. Studies of this pathway in Brucella abortus support a model in which phosphorylation of PhyR is controlled by two HWE-family sensor kinases: LovhK and Bab1_1673. PhyR phosphorylation promotes its binding to NepR, which releases σ^E1 to control transcription of select cell envelope genes that influence in vitro stress survival and host infection. The LOV and PAS sensory domains of the cytoplasmic GSR-activating kinase, LovhK, are labeled. The periplasmic CHASE family sensor domain of the transmembrane GSR-repressive kinase, Bab1_1673, is labeled. Solid lines indicate a direct interaction; dashed lines indicate interactions that may be direct or indirect. (b) Brucella spp. BvrR/BvrS is a conserved, archetypal two-component system that is a critical regulator of infection. In response to detection of intracellular signals during infection, the histidine kinase BvrS phosphorylates BvrR, which then regulates transcription of a suite of cell envelope and metabolic genes important for intracellular survival and replication. Abbreviations: DBD, DNA-binding domain; GSR, general stress response; REC, REC, receiver domain; RNAP, RNA polymerase; OMP, outer membrane protein.