Initiation of translation makes attenuation of ampC in E. coli dependent on growth rate.
The chromosomal beta-lactamase gene of E. coli, ampC, shows increased expression with increased growth rate of the bacteria. We have previously shown that transcription of ampC is attenuated, and that a mutation in the terminator stem of this attenuator abolishes the growth rate-dependency of ampC expression. We now present studies using mutations, made in vitro, located such that the 5'-end of ampC mRNA carries a possible recognition sequence for initiation of translation close to the attenuator stem. Alteration of the supposed initiation codon AUG to UUG resulted in a reduced and growth rate-independent expression of ampC beta-lactamase. AmpC mRNA starts with the sequence AUC, which might be a non-typical ribosome binding site, situated four bases before the AUG. Deletion of the C in this sequence caused a partial reduction of ampC expression and also a partial loss of the growth rate-dependent regulation. The phenotypes of these mutants support a model in which formation of a ribosome initiation complex at a level increasing with the growth rate inhibits termination of transcription at the ampC attenuator.
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D005786:Gene Expression Regulation; D014176:Protein Biosynthesis; D012270:Ribosomes / Q000502:physiology; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
D001426:Bacterial Proteins; D001618:beta-Lactamases