title: Regulation of pyrBI operon expression in Escherichia coli by UTP-sensitive reiterative RNA synthesis during transcriptional initiation.
abstract: 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.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham 35294.
authors.forename: C
authors.initials: C
authors.lastname: Liu
authors.forename: L S
authors.initials: LS
authors.lastname: Heath
authors.forename: C L
authors.initials: CL
authors.lastname: Turnbough
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D003062:Codon; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005838:Genotype; D007700:Kinetics; D016296:Mutagenesis; D009876:Operon; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000096:biosynthesis*; D011995:Recombination, Genetic; D013698:Templates, Genetic; D014158:Transcription, Genetic; D014544:Uridine Triphosphate / Q000378:metabolism*
chemical_list: D003062:Codon; D012329:RNA, Bacterial; D012321:DNA-Directed RNA Polymerases; D014544:Uridine Triphosphate