ROLE OF THE PROMOTER IN ACTIVATION OF TRANSCRIPTION BY NITROGEN REGULATOR-I PHOSPHATE IN ESCHERICHIA-COLI

The protein nitrogen regulator I (NR1)-phosphate is known to activate the initiation of transcription of the Escherichia coli glnA gene. This activation is facilitated by the binding of the protein to NR1-specific sites located upstream of the σ54-dependent glnA promoter. To determine whether binding of NR1-phosphate to upstream sites is sufficient for activation, we placed several promoters not normally activated by NR1-phosphate downstream of NR1 binding sites and measured activation in intact cells and in an in vitro transcription system. We found that the σ70-dependent lac promoter was not activated, that the σ54-dependent Klebsiella pneumoniae nifH promoter was weakly activated, and that a nifH promoter altered in the RNA polymerase binding site was almost as well activated as the glnA promoter. We conclude that the sensitivity of the susceptible promoter depends on the presence of NR1 binding sites, but that the presence of bound NR1-phosphate upstream of a promoter is not sufficient for activation of transcription by RNA polymerase. This activation is determined by the structure of the RNA polymerase binding site. We suggest that σ54- but not σ70-dependent promoters are susceptible to activation by NR1-phosphate and that the nucleotide sequence of the σ54-RNA polymerase binding site is an important determinant of the efficiency of activation.