Transcription factor that mediates regulation of both acid- and alkaline-expressed genes in response to ambient pH. At alkaline ambient pH, activates transcription of alkaline-expressed genes (including pacC itself) and represses transcription of acid-expressed genes. Specifically recognizes and binds the consensus sequence 5'-GCCARG-3'. May act as a negative regulator of virulence to plants. By alkaline conditions and during infection of tomato roots. Activated by C-terminal proteolytic cleavage. At neutral to alkaline ambient pH, the signaling protease cleaves pacC within the conserved 24-residue signaling protease box. In an ambient pH-independent reaction, the processing protease (probably the proteasome) removes additional C-terminal residues to yield the functional form. Belongs to the pacC/RIM101 family.