Figure 3. Activation of σ^B by different stresses leads to distinct responses.

Activation of σ^B by environmental stress (e.g., EtOH, blue) and energy stress (decreased NTP, orange) lead to two different σ^B behaviors: EtOH induces a coordinated response, while nucleotide limitation induces stochastic pulses (same maximum amplitude) on a single-cell level. σ^B is inhibited by RsbW, which is in turn inhibited by RsbV. RsbW, a kinase, phosphorylates RsbV to relieve its own inhibition. Countering this, stress-specific phosphatases such as RsbTU (activated by EtOH, blue) and RsbQP (activated by NTP limitation, orange) dephosphorylate RsbV~P, allowing RsbV to bind to and inhibit RsbW and thereby promoting release and activation of σ^B.