Translation activates the paused transcription complex and restores transcription of the trp operon leader region

Abstract

It has been proposed that RNA polymerase pausing in the leader region of the tryptophan (trp) operon of Escherichia coli is responsible for the synchronization of transcription and translation essential to attenuation control. In this report we use an in vitro coupled transcription/translation system to study the effect of trp leader peptide synthesis on RNA polymerase pausing in the trp leader region. Wild-type and translation-defective trp leader templates of E. coli and Serratia marcescens were employed, and pause RNA synthesis and paused complex release (activation) were quantified relative to synthesis of the terminated leader transcript. It was observed that pausing in the trp leader region was prolonged when translation of the leader transcript was reduced by mutations in the leader region or by addition of the translation inhibitor kasugamycin or chloramphenicol. Experiments with S-30 extracts from a mutant strain that is inefficient in translating the tryptophan codons in the leader transcript indicated that ribosome movement to these codons also releases the paused transcription complex. These findings indicate that the paused trp leader transcription complex resumes transcription when released by ribosome movement over the leader peptide coding region. This release would facilitate the coupling of transcription and translation essential to attenuation control.