Interaction between GlnB and the N-terminal domain of NifA in Azospirillum brasilense

Azospirillum brasilense is a diazotroph associated with many important agricultural crops and shows potential as a biofertilizer. NifA, the transcriptional activator of nitrogen fixation (nif) genes, and GlnB, one of PII signal transduction family protein, are key proteins in the regulation of nitrogen fixation in A. brasilense. It was previously reported that the regulation of NifA activity in A. brasilense depends on GlnB. We report here that GlnB was found to interact directly with the N-terminal domain of NifA in vivo under nitrogen-free conditions and the N-terminal mutant of NifA in which the Tyr residues at position 18 and 53 were replaced by Phe (NifA-N-Y18/53F) strengthened the interaction with GlnB. Moreover, we also found that the amino acid residues 66―88 and 165―176 in N-terminus of NifA are responsible for the interaction with GlnB.