Fig. 1.
Model of the σB signalling network in L. monocytogenes, derived from that of the B. subtilis network (see text), but with only one input phosphatase, RsbU. The large stressosome complex is simplified to show only the core components RsbR, RsbS and RsbT. We present evidence that environmental (or physical) stresses enter the network upstream from RsbU. These stresses are thought to induce RsbT kinase activity within the stressosome, leading to phosphorylation of the RsbR and RsbS antagonists; this phosphorylation frees RsbT to bind and activate RsbU by direct protein–protein interaction. By contrast, our data suggest that energy (or nutritional) stresses enter the network downstream from RsbU; these stresses would diminish RsbW kinase activity as ATP levels fall. In this scheme, the RsbX feedback phosphatase has no direct role in stress response but returns the system to its ground state following an environmental stress.