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, 198 (3), 411-5

Initiation of Translation Makes Attenuation of ampC in E. Coli Dependent on Growth Rate

Initiation of Translation Makes Attenuation of ampC in E. Coli Dependent on Growth Rate

T Grundström et al. Mol Gen Genet.

Abstract

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.

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