Regulation of the synthesis of glutamine synthetase by the PII protein in Klebsiella aerogenes.

Certain mutations at the glaB locus result in the failure to fully derepress glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] and to convert it to the active nonadenylylated form in response to nitrogen limitation. In these mutants the PII regulatory protein is altered such that it cannot be converted by uridylyltransferase to the form stimulating deadenylylation of glutamine synthetase by adenylyltransferase. Additional mutations as well as insertions of transposon Tn5 at the glnB site result in the loss of PII. The loss of PII does not prevent adenylylation and deadenylylation of glutamine synthetase but reduces the rates of these reactions. Cells lacking PII have a high level of glutamine synthetase even when they are grown with an excess of ammonia and the enzyme is highly adenylylated. The results suggest that the PII protein plays a role, independent of its effect on adenylylation, in the regulation of the level of glutamine synthetase.