Fig 4.

Model of the signal transduction network leading to the activation of σ^B. Under physiological conditions, most σ^B molecules are sequestered by the antisigma factor RsbW, which also acts as a kinase to phosphorylate the anti-antisigma factor RsbV to keep it inactive. Energy stress leads to the dephosphorylation of the anti-antisigma factor RsbV by the RsbP phosphatase, whereas environmental (physical) stress activates the RsbU phosphatase. Dephosphorylated RsbV will attack the RsbW-σ^B complex, leading to the release of the sigma factor, which is now able to transcribe all the genes of the σ^B regulon. For further details, see text