Regulatory mutations in the Klebsiella aerogenes structural gene for glutamine synthetase

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Abstract
Glutamine synthetase could be repressed several hundredfold rather than 6- to 10-fold as previously reported. NH3 was not the primary repression signal for glutamine synthetase. Repression appeared to be mediated by a high level of glutamine and probably by a high ratio of glutamine to .alpha.-ketoglutarate. Mutations in glnA (the structural gene for glutamine synthetase) were seen to fall into 3 phenotypic groups: glutamine auxotrophs that produced no detectable glnA product; glutamine auxotrophs that produced a glnA product lacking enzymatic activity (and hence repressibility by NH3) but were repressible under appropriate conditions; and glutamine synthetase regulatory mutants, whose glnA product was enzymatically active and not repressible under any conditions.

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