Spx is a global transcriptional regulator in Bacillus subtilis that mediates oxidative stress responses through interactions with the RNA polymerase α subunit C-terminal domain (αCTD). This study shows that Spx negatively regulates ComA-dependent transcription by competing for overlapping binding sites in the α1 region of αCTD, including residues Y263, C265, and K267. Oxidized Spx enhances but is not required for negative control. Spx abundance is regulated by ClpXP proteolysis, which is inhibited under disulfide stress via disruption of the ClpX zinc-binding domain. YjbH acts as a specific post-translational negative regulator of Spx.
