Involved in the regulation of nitrogen metabolism (PubMed:17203075). Regulates the activity of its targets by protein-protein interaction in response to the nitrogen status of the cell (PubMed:17203075). Regulates the activity of the ammonia channel Amt1 via direct interaction (PubMed:17203075). Formation of the GlnK1/Amt1 complex is decreased in the presence of Mg-ATP or 2-oxoglutarate. The presence of both effectors abolishes the formation of the complex. Homotrimer (PubMed:17203075). Interacts and forms a complex with Amt1 (PubMed:17203075). Belongs to the P(II) protein family.