The transmembrane ammonium transporters (Amts) are believed to be involved in scavenging and recapturing ammonium that diffuses out of eukaryotic and prokaryotic cells under conditions where nitrogen is low. In bacteria, the amtB gene is in an operon with glnK, a gene encoding a signal transduction protein that acts as a nitrogen sensor. GlnK is a trimer that is uridylylated on Tyr51 in response to nitrogen deficiency. Coutts et al. determined that GlnK and Amt interact, which is responsible for the localization of GlnK to the membrane. GlnK is deuridylylated upon ammonia shock (the addition of ammonium to nitrogen-limited medium), and the unmodified GlnK is the one that interacts most strongly with Amt under nitrogen-replete conditions. Binding of GlnK appeared to inhibit ammonium transport, because strains of bacteria lacking the glnK gene exhibited higher basal transport rates than did wild-type bacteria. Thus, it appears that when nitrogen concentrations are sufficient, GlnK is deuridylylated and interacts with Amt to inhibit the recapture of ammonium from the medium.