Phosphorylation of nitrogen regulator I of Escherichia coli induces strong cooperative binding to DNA essential for activation of transcription

The affinities of nitrogen regulator I (NR I) and of NRI-phosphate for single binding sites were compared with the affinities for sites 1 and 2 located upstream from gInAp2. The measurements were then correlated with the ability of NRI-phosphate to activate transcription of glnAp2. Results show that NRI is not enough for sufficient activation and that activation occurs only at higher NRI concentration. The phosphorylation of NRI is perceived to induce a conformational change in the N-terminal domains of theNRI-phosphate dimers which interact strongly with each other.