A 750 bp sensory integration region directs global control of the Escherichia coli GadE acid resistance regulator

Escherichia coli survives pH 2 environments through an acid resistance (AR) system regulated by the transcriptional activator GadE. Numerous proteins control gadE at an upstream, conserved, 798 bp intergenic region. We show this region produces three transcripts starting at -124 (T1), -324/-317 (T2) and -566 (T3) bp from the gadE start codon. Transcriptional lacZ fusions to gadE promoter regions revealed P1 and P3 were active while P2 alone was not. However, pairing P3 with P2 activated P2 and increased expression 20-fold above P3 alone. The fusions were transferred to Salmonella, which lacks this AR system, and plasmid-borne E. coli-specific regulators EvgA, YdeO, GadE and GadX were introduced. Data revealed that YdeO and GadX activate P3, P2 and P3P2, while GadE autoactivates P1 and represses P3 and P3P2. The developing model indicates that different signals activate YdeO, GadX, or an MnmE-dependent regulator, which stimulate gadE transcription from the P3 and P2 promoters. Once made, GadE activates P1 and represses P3 and P2. The P1 region also enables efficient downstream transcription and translation of the P3 or P2 transcripts. Evidence indicates the entire 750 bp sensory integration locus is necessary for a versatile response.