Regulation of pyrBI operon expression in Escherichia coli by UTP-sensitive reiterative RNA synthesis during transcriptional initiation.

Academic Article


  • Pyrimidine-mediated regulation of pyrBI operon expression in Escherichia coli K-12 occurs through UTP-sensitive transcriptional attenuation and through a second mechanism that functions at the level of transcriptional initiation. In this study we demonstrate that this second control mechanism is based on UTP-sensitive reiterative RNA synthesis within a run of three T-A base pairs in the pyrBI initially transcribed region. Our results show that high UTP levels induce the synthesis in vitro of nascent transcripts with the sequence AAUUUUn (where n = 1 to > 30), which are not extended downstream to include pyrBI sequences. Synthesis of these transcripts, which are initiated at the predominant in vivo transcriptional start site, inhibits the production of full-length pyrBI transcripts. A TTT to GTA mutation in the pyrBI initially transcribed region eliminates reiterative transcription and stimulates productive transcription in vitro. When introduced into the E. coli chromosome, this mutation causes a sevenfold increase in pyrBI expression in cells grown under conditions of pyrimidine excess and nearly abolishes pyrimidine-mediated regulation of pyrBI expression when coupled with a mutation that eliminates attenuation control. Additional experiments indicate that the context of the three T-A base pairs within the pyrBI initially transcribed region is important for reiterative transcription. A possible mechanism for reiterative transcription and the likely involvement of this process in the regulation of other genes are discussed.
  • Published In


  • Base Composition, Base Sequence, Codon, DNA-Directed RNA Polymerases, Escherichia coli, Gene Expression Regulation, Bacterial, Genotype, Kinetics, Mutagenesis, Operon, Plasmids, Promoter Regions, Genetic, RNA, Bacterial, Recombination, Genetic, Templates, Genetic, Transcription, Genetic, Uridine Triphosphate
  • Digital Object Identifier (doi)

    Author List

  • Liu C; Heath LS; Turnbough CL
  • Start Page

  • 2904
  • End Page

  • 2912
  • Volume

  • 8
  • Issue

  • 23