Involvement of the product of the glnF gene in the autogenous regulation of glutamine synthetase formation in Klebsiella aerogenes

Abstract

Mutations in a site, glnF, linked by [phage] P1-mediated transduction to argG on the chromosome of K. aerogenes, result in a requirement for glutamine. Mutants in this gene have in all media a level of glutamine synthetase (GS) corresponding to the level found in the wild-type strain grown in the medium producing the strongest repression of GS. The adenylylation and deadenylylation of GS in glnF mutants is normal. The glutamine requirement of glnF mutants could be suppressed by mutations in the structural gene for GS, glnA. These mutations resulted in altered regulation of GS synthesis, regardless of the presence or absence of the glnF mutation (GlnR phenotype). In GlnR mutants the GS level is higher than in the wild-type strain when the cells are cultured in strongly repressing medium, but lower than in the wild-type strain when the cells are cultured in a derepressing medium. Heterozygous merodiploids carrying a normal glnA gene and a glnA gene responsible for the GlnR phenotype behave in every respect like merodiploids carrying 2 normal glnA genes. These results confirm autogenous regulation of GS synthesis and indicate that GS is both a repressor and an activator of GS synthesis. The mutation in glnA responsible for the GlnR phenotype apparently resulted in the formation of a GS that is incompetent both as repressor and as activator of GS synthesis. According to this hypothesis, the product of the glnF gene is necessary for activation of the glnA gene by CS.