ABSTRACTBacteria possess multiple mechanisms to survive exposure to various chemical stresses and antimicrobial compounds. In the enteric bacteriumEscherichia coli, three homologous transcription factors—MarA, SoxS, and Rob—play a central role in coordinating this response. Three separate systems are known to regulate the expression and activities of MarA, SoxS, and Rob. However, a number of studies have shown that the three do not function in isolation but rather are coregulated through transcriptional cross talk. In this work, we systematically investigated the extent of transcriptional cross talk in themar-sox-robregulon. While the three transcription factors were found to have the potential to regulate each other's expression when ectopically expressed, the only significant interactions observed under physiological conditions were betweenmarandrobsystems. MarA, SoxS, and Rob all activate themarRABpromoter, more so when they are induced by their respective inducers: salicylate, paraquat, and decanoate. None of the three proteins affects thesoxSpromoter, though unexpectedly, it was mildly repressed by decanoate by an unknown mechanism. SoxS is the only one of the three proteins to repress therobpromoter. Surprisingly, salicylate somewhat activates transcription ofrob, while decanoate represses it a bit. Rob, in turn, activates not only its downstream promoters in response to salicylate but also themarRABpromoter. These results demonstrate that themarandrobsystems function together in response to salicylate.
Transcriptional Cross Talk within themar-sox-robRegulon in Escherichia coli Is Limited to therobandmarRABOperons
