Fig. 5.

Model of partner-switching mechanism controlling general stress response in M. extorquens. In unstressed cells, PhyR is inactive, and the ECF sigma factor σ^EcfG1 is sequestered by its anti-sigma factor, NepR. In response to a stress, PhyR is phosphorylated and interacts with NepR, thus releasing σ^EcfG1 and allowing σ^EcfG1 to associate with RNA polymerase to transcribe stress genes. Note that additional σ^EcfG sigma factors are likely to be involved in PhyR dependent stress response (see Discussion for further details).