This is a family of bifunctional uridylyl-removing enzymes/uridylyltransferases (UR/UTases, GlnD) that are responsible for the modification (EC:2.7.7.59) of the regulatory protein P-II, or GlnB (e.g. Swiss:P05826, Pfam:PF00543). In response to nitrogen limitation, these transferases (e.g. Swiss:P27249) catalyse the uridylylation of the PII protein, which in turn stimulates deadenylylation of glutamine synthetase (GlnA). Deadenylylated glutamine synthetase is the more active form of the enzyme [1]. Moreover, uridylylated PII can act together with NtrB and NtrC to increase transcription of genes in the sigma54 regulon, which include glnA and other nitrogen-level controlled genes [2]. It has also been suggested that the product of the glnD gene is involved in other physiological functions such as control of iron metabolism in certain species [2]. The region described in this family is found in many of its members to be C-terminal to a nucleotidyltransferase domain (Pfam:PF01909), and N-terminal to an HD domain (Pfam:PF01966) and two ACT domains (Pfam:PF01842) [3].

1: The genes of the glutamine synthetase adenylylation cascade are not regulated by nitrogen in Escherichia coli. van Heeswijk WC, Rabenberg M, Westerhoff HV, Kahn D; Mol Microbiol 1993;9:443-457. PMID:8412694

2: Novel effects of a transposon insertion in the Vibrio fischeri glnD gene: defects in iron uptake and symbiotic persistence in addition to nitrogen utilization. Graf J, Ruby EG; Mol Microbiol 2000;37:168-179. PMID:10931314

3: Isolation and characterization of the glnD gene of Gluconacetobacter diazotrophicus, encoding a putative uridylyltransferase/uridylyl-removing enzyme. Perlova O, Nawroth R, Zellermann EM, Meletzus D; Gene 2002;297:159-168. PMID:12384297