OLIGOMERIZATION OF NTRC AT THE GLNA ENHANCER IS REQUIRED FOR TRANSCRIPTIONAL ACTIVATION

To activate transcription of the glnA gene, the dimeric NTRC protein ( nitrogen regulatory protein C) of enteric bacteria binds to an enhance r located approximately 100 bp upstream of the promoter. The enhancer is composed of two binding sites for NTRC that are three turns of the DNA helix apart. One role of the enhancer is to tether NTRC in high lo cal concentration near the promoter to allow for its frequent interact ion with sigma54 holoenzyme by DNA looping. We have found that a secon d role of the enhancer is to ensure oligomerization of NTRC into a com plex of at least two dimers that is required for transcriptional activ ation. Formation of this complex is greatly facilitated by a protein-p rotein interaction between NTRC dimers that is increased when the prot ein is phosphorylated.