Involved in the regulation of nitrogen metabolism (PubMed:21265784, PubMed:23420616). Regulates the activity of its targets by protein-protein interaction in response to the nitrogen status of the cell (PubMed:23069245). Increases the activity of the glutamine synthetase 3 in the presence of 2-oxoglutarate (PubMed:23069245). May regulate the activity of the ammonia channel Amt2 via direct interaction (By similarity). Binds the effectors ADP and ATP. Also binds AMP with high affinity, raising the possibility that AMP could be an important PII effector, at least in archaea. The change in the ATP/AMP ratio may be more relevant for describing the energy status in the cells than the ATP/ADP ratio alone. Homotrimer (PubMed:23069245, PubMed:24946894). Interacts with the glutamine synthetase 3 (GS3) in the presence of 2-oxoglutarate (PubMed:23069245). Interacts in vitro with Amt1 after ammonium shock (PubMed:24039236). May also interact with Amt2 (PubMed:24039236). Expressed during ammonium starvation under nitrate-rich conditions. Uridylylated on Tyr-62. Belongs to the P(II) protein family.