title: gltBDF operon of Escherichia coli.
abstract: A 2.0-kilobase DNA fragment carrying antibiotic resistance markers was inserted into the gltB gene of Escherichia coli previously cloned in a multicopy plasmid. Replacement of the chromosomal gltB+ gene by the gltB225::omega mutation led to cells unable to synthesize glutamate synthase, utilize growth rate-limiting nitrogen sources, or derepress their glutamine synthetase. The existence of a gltBDF operon encoding the large (gltB) and small (gltD) subunits of glutamate synthase and a regulatory peptide (gltF) at 69 min of the E. coli linkage map was deduced from complementation analysis. A plasmid carrying the entire gltB+D+F+ operon complemented cells for all three of the mutant phenotypes associated with the polar gltB225::omega mutation in the chromosome. By contrast, plasmids carrying gltB+ only complemented cells for glutamate synthase activity. A major tricistronic mRNA molecule was detected from Northern (RNA blot) DNA-RNA hybridization experiments with DNA probes containing single genes of the operon. A 30,200-dalton polypeptide was identified as the gltF product, the lack of which was responsible for the inability of cells to use nitrogen-limiting sources associated with gltB225::omega.
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005970:Glutamate Synthase / Q000235:genetics* / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009693:Nucleic Acid Hybridization; D009876:Operon; D010641:Phenotype; D010957:Plasmids; D012329:RNA, Bacterial / Q000235:genetics; D000637:Transaminases / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004269:DNA, Bacterial; D012329:RNA, Bacterial; D014157:Transcription Factors; D005970:Glutamate Synthase; D000637:Transaminases; D005974:Glutamate-Ammonia Ligase