Regulation of expression from the glnA promoter of Escherichia coli in the absence of glutamine synthetase.

One of the suspected regulators of glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] in enteric bacteria is glutamine synthetase itself. We isolated Escherichia coli strains carrying fusions of the beta-galactosidase structural gene to the promoter of the glutamine synthetase gene, with the aid of the Casadaban Mud1 (ApR, lac, cts62) phage. Some aspects of regulation were retained in haploid fusion strains despite the absence of glutamine synthetase, whereas other aspects required glutamine synthetase catalytic or regulatory activity or both. The direction of transcription of the glutamine synthetase gene was also determined.