The ArgR regulatory protein, a helper to the anaerobic regulator ANR during transcriptional activation of the arcD promoter in Pseudomonas aeruginosa

Pseudomonas aeruginosa, when deprived of oxygen, generates ATP from arginin e catabolism by enzymes of the arginine deiminase pathway, encoded by the a rcDABC operon, Under conditions of low oxygen tension, the transcriptional activator ANR binds to a site centered 41.5 bp upstream of the arcD transcr iptional start, ANR-mediated anaerobic induction was enhanced two- to three fold by extracellular arginine, This arginine effect depended, in trans, on the transcriptional regulator ArgR and, in cis, on an ArgR binding site ce ntered at -73.5 bp in the arcD promoter, Binding of purified ArgR protein t o this site was demonstrated by electrophoretic mobility shift assays and D Nase I footprinting. This ArgR recognition site contained a sequence, 5'-TG ACGC-3', which deviated in only I base from the common sequence motif 5'-TG TCGC-3' found in other ArgR binding sites of P. aeruginosa. Furthermore, an alignment of all known ArgR binding sites confirmed that they consist of t wo directly repeated half-sites, In the absence of ANR, arginine did not in duce the are operon, suggesting that ArgR alone does not activate the arcD promoter. According to a model proposed, ArgR makes physical contact with A NR and thereby facilitates initiation of are transcription.