Required for full induction of the nrgAB operon under conditions of ammonium limitation. Needs to interact with NrgA in order to localize correctly to the membrane. The nrgAB operon is activated by TnrA under nitrogen-limited conditions. Cells show no growth phenotype even at acidic pH. Belongs to the P(II) protein family. It is uncertain whether Met-1 or Met-5 is the initiator.