FIG. 5.

Model for the transcriptional regulation of the mPH operon in C. testosteroni R5. (A) Expression of the Phc mPH operon in the presence of the genuine substrate for mPH. PhcR-mediated transcriptional activation of the Phc mPH operon was enhanced by PhcT-mediated regulation, while transcription of phcR was largely inhibited by this regulation. The action of PhcS was prevented by factor X. In the absence of PhcT, PhcR-mediated transcriptional activation was not enhanced, and the inhibition of phcR transcription was relieved. (B) Expression of the Phc mPH operon in the absence of the genuine substrate for mPH. PhcR-mediated transcriptional activation of the Phc mPH operon was repressed by PhcS (38). PhcT was not involved in the gratuitous expression which occurred in strain R5S in the absence of the genuine substrate for mPH.