Involved in the regulation of nitrogen metabolism (By similarity). Regulates the activity of its targets by protein-protein interaction in response to the nitrogen status of the cell (By similarity). Regulates the activity of the ammonia channel Amt1 via direct interaction (By similarity). Homotrimer (PubMed:21301082). Interacts and forms a complex with Amt1 (By similarity). Belongs to the P(II) protein family.