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

Microbiology (Reading). 1995 May:141 ( Pt 5):1085-1092. doi: 10.1099/13500872-141-5-1085.

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Chromosome Mapping
  • Chromosomes, Bacterial
  • DNA Primers
  • Escherichia coli / drug effects
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Genes, Bacterial
  • Genotype
  • Membrane Proteins / biosynthesis
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins*
  • Methylnitronitrosoguanidine / pharmacology
  • Molecular Sequence Data
  • Mutagenesis
  • Point Mutation*
  • Polymerase Chain Reaction
  • Restriction Mapping
  • Signal Transduction*
  • beta-Lactamases / biosynthesis*
  • beta-Lactams

Substances

  • AmpG protein, Bacteria
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • DNA Primers
  • Membrane Proteins
  • Membrane Transport Proteins
  • beta-Lactams
  • Methylnitronitrosoguanidine
  • beta-Lactamases

Associated data

  • GENBANK/X82158
  • GENBANK/X82159
  • GENBANK/X82160