We have investigated the expression and regulation of the ECF sigma factor encoded by the sigW gene. Expression of sigW is regulated by both growth phase and medium composition.
Maximal expression is attained in early stationary phase cells grown in rich medium.
Thus, these two regulons are mutually antagonistic. Reconstituted SigW holoenzyme faithfully recognizes the PW preceding sigW but does not recognize the PX promoter preceding the sigX gene. In contrast, several promoters that are at least partially under SigX control are active with both the SigX and SigW holoenzymes in vitro. This supports the suggestion that the SigW and SigX regulons overlap.