Attenuation in the rph‐pyrE operon of Escherichia coli and processing of the dicistronic mRNA

Abstract

We have substituted on a plasmid the native promoter of the Escherichia coli rph‐pyrE operon with an inducible transcription‐initiation signal. The plasmid was used to study the mRNA chains derived from the operon at different intracellular concentrations of UTP and as a function of time following induction of transcription. The results showed that dicistronic rph‐pyrE mRNA was formed when the UTP pool was low, and that a monocistronic rph mRNA was the major transcription product in high‐UTP pools, thus supporting an UTP‐controlled attenuation mechanism for regulation of pyrE gene expression. However, the dicistronic rph‐pyrE transcript was rapidly processed into two monocistronic mRNA units, and a cleavage site was mapped near the attenuator in the intercistronic region, close to the site where transcription was terminated in high‐UTP pools. Furthermore, the major 3′ end of the pyrE mRNA was mapped near a palindromic structure of similarity to the family of repetitive extragenic palindromic sequences, 35 nucleotide residues after the stop codon of the pyrE gene. Copyright © 1992, Wiley Blackwell. All rights reserved