In nitrogen-limiting conditions, when the ratio of Gln to 2-ketoglutarate decreases, P-II is uridylylated to P-II-UMP. P-II-UMP allows the deadenylation of glutamine synthetase (GS), thus activating the enzyme. Conversely, in nitrogen excess P-II is deuridylated and promotes the adenylation of GS. P-II indirectly controls the transcription of the GS gene (glnA). P-II prevents NR-II-catalyzed conversion of NR-I to NR-I-phosphate, the transcriptional activator of glnA. When P-II is uridylylated to P-II-UMP, these events are reversed. Homotrimer. Belongs to the P(II) protein family.