Transcriptional pausing at the translation start site operates as a critical checkpoint for riboswitch regulation

Nat Commun. 2017 Jan 10;8:13892. doi: 10.1038/ncomms13892.

Abstract

On the basis of nascent transcript sequencing, it has been postulated but never demonstrated that transcriptional pausing at translation start sites is important for gene regulation. Here we show that the Escherichia coli thiamin pyrophosphate (TPP) thiC riboswitch contains a regulatory pause site in the translation initiation region that acts as a checkpoint for thiC expression. By biochemically probing nascent transcription complexes halted at defined positions, we find a narrow transcriptional window for metabolite binding, in which the downstream boundary is delimited by the checkpoint. We show that transcription complexes at the regulatory pause site favour the formation of a riboswitch intramolecular lock that strongly prevents TPP binding. In contrast, cotranscriptional metabolite binding increases RNA polymerase pausing and induces Rho-dependent transcription termination at the checkpoint. Early transcriptional pausing may provide a general mechanism, whereby transient transcriptional windows directly coordinate the sensing of environmental cues and bacterial mRNA regulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Codon, Initiator
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Gene Expression Regulation, Bacterial
  • Mutation
  • Protein Biosynthesis
  • Protein Conformation
  • Ribonuclease H / genetics
  • Ribonuclease H / metabolism
  • Riboswitch / genetics*
  • Thiamine Pyrophosphate / metabolism
  • Transcription, Genetic

Substances

  • Bacterial Proteins
  • Codon, Initiator
  • Escherichia coli Proteins
  • Rho protein, E coli
  • Riboswitch
  • ThiC protein, Bacteria
  • Ribonuclease H
  • Thiamine Pyrophosphate