THE HOMOLOGOUS REGULATORS ANR OF PSEUDOMONAS-AERUGINOSA AND FNR OF ESCHERICHIA-COLI HAVE OVERLAPPING BUT DISTINCT SPECIFICITIES FOR ANAEROBICALLY INDUCIBLE PROMOTERS

The anaerobic transcriptional regulator ANR induces the arginine deimi nase and denitrification pathways in Pseudomonas aeruginosa during oxy gen limitation. The homologous activator FNR of Escherichia coli, when introduced into an anr mutant of P. aeruginosa, could functionally re place ANR for anaerobic growth on nitrate but not for anaerobic induct ion of arginine deiminase. In an FNR-positive E. coli strain, the ANR- dependent promoter of the arcDABC operon, which encodes the enzymes of the arginine deiminase pathway, was not expressed. To analyse systema tically these distinct induction patterns, a lacZ promoter-probe, broa d-host-range plasmid containing various -40 regions (the ANR/FNR recog nition sequences) and -10 promoter sequences was constructed. These co nstructs were tested in P. aeruginosa and in E. coli expressing either ANR or FNR. In conjunction with the consensus -10 hexamer of E. coli sigma(70) RNA polymerase (TATAAT), the consensus FNR site (TTGAT....AT CAA) was recognized efficiently by ANR and FNR in both hosts. By contr ast, when promoters contained the Are box (TTGAC....ATCAC), which is f ound in the arcDABC promoter. or a symmetrical mutant FNR site (CTGAT. ...ATCAG), ANR was a more effective activator than was FNR. Conversely , an extended 22 bp, fully symmetrical FNR site allowed better activat ion with FNR than with ANR. Combination of the are promoter -10 sequen ce (CCTAAT) with the Are box or the consensus FNR site resulted in goo d ANR-dependent expression in P. aeruginosa but gave practically no ex pression in E. coli, suggesting that RNA polymerase of P. aeruginosa d iffers from the E. coli enzyme in -10 recognition specificity. In conc lusion, ANR and FNR are able to activate the RNA polymerases of P. aer uginosa and E. coli when the -40 and -10 promoter elements are identic al or close to the E. coli consensus sequences.