MtrR and FarR regulation of glnA expression. The specific activity of β-Gal (expressed as nanomoles of o-nitrophenyl-β-d-galactopyranoside hydrolyzed per mg of protein) in strains PJ9 (FA19 glnA::lacZ), PJ10 (JF1 glnA::lacZ), PJ12 (JF6 glnA::lacZ), PJ11 (EL24 glnA::lacZ), PJ14 (EL28 glnA::lacZ), PJ13 (PJ10 farR::kn glnA lacZ), PJ15 (PJ14 farR+), and PJ22 (PJ13 mtrR+). The results are shown as an average value (± standard deviation) from three independent experiments. The single asterisk above a bar denotes a significant (P < 0.01) difference between the indicated strain and wild-type strain PJ9, while the double asterisk denotes a significant difference (P < 0.01) between a complemented strain and its respective mutant (comparisons of PJ12 versus PJ10, PJ14 versus PJ11, and PJ15 versus PJ13); the specific P values are provided in the text.