title: The signal transducer encoded by ampG is essential for induction of chromosomal AmpC beta-lactamase in Escherichia coli by beta-lactam antibiotics and 'unspecific' inducers.
abstract: Chemical mutagenesis of the AmpC beta-lactamase-hyperinducible Escherichia coli strain SN0301/pNu305 carrying the cloned ampC and ampR genes from Citrobacter freundii OS60 gave four independent mutants in which beta-lactamase was no longer inducible, or was inducible only to a low level, by beta-lactam antibiotics. The genes ampC, ampR, ampD and ampE, which were essential for beta-lactamase induction, were functional in these mutants. In all four mutants, the sites of mutation were mapped to 9.9 min on the E. coli chromosome. Complementation with wild-type ampG restored inducibility of beta-lactamase to wild-type levels. The nucleotide sequence of all four mutant ampG alleles (ampG1, ampG3, ampG4 and ampG5) was determined. In three of the mutants, a single base exchange led to an amino acid change from glycine to aspartate at different sites in the deduced amino acid sequence. In the fourth mutant (ampG4), with low-level inducibility, the nucleotide sequence was identical to wild-type ampG. Spontaneous back-mutation of the chromosomal ampG1 mutant resulted in restoration of wild-type inducibility and a return to the wild-type ampG sequence. Unspecific induction by components of the growth medium was also dependent on intact ampG function.
authors.affiliation: Institut fr Mikrobiologie, Technische Hochschule, 64287 Darmstadt, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: Bayer AG, 51368 Leverkusen, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Korfmann
authors.affiliation: Institut fr Mikrobiologie, Technische Hochschule, 64287 Darmstadt, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Barth
authors.affiliation: Institut fr Mikrobiologie, Technische Hochschule, 64287 Darmstadt, Germany.
authors.forename: Hans H
authors.initials: HH
authors.lastname: Martin
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000378:metabolism*; D001483:Base Sequence; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D017931:DNA Primers; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D005838:Genotype; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D015183:Restriction Mapping; D015398:Signal Transduction; D001618:beta-Lactamases / Q000096:biosynthesis*; D047090:beta-Lactams
chemical_list: C084284:AmpG protein, Bacteria; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D017931:DNA Primers; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D047090:beta-Lactams; D008769:Methylnitronitrosoguanidine; D001618:beta-Lactamases