Activation of the Bacillus subtilis spoIIG promoter requires interaction of Spo0A and the sigma subunit of RNA polymerase.

Bacillus subtilis Spo0A activates transcription from both sigmaA- and sigmaH-dependent promoters. Baldus et al. (2) identified two amino acid substitutions in the carboxyl terminus of sigmaA, K356E and H359R, that specifically impaired Spo0A-activated transcription in vivo. To test the model in which the K356E and H359R substitutions in sigmaA interfere with the interaction of Spo0A and sigmaA, we examined the effects of alanine substitutions at these positions in sigmaA on sigmaA's ability to direct transcription in vivo and in vitro. We found that alanine substitutions at these positions specifically reduced expression from the sigmaA-dependent, Spo0A-dependent promoters, spoIIG and spoIIE, in vivo. Furthermore, we found that stimulation of spoIIG promoter activity by Spo0A in vitro was reduced by the single substitutions H359A and H359R in sigmaA.