title: DNA supercoiling-dependent transcriptional coupling between the divergently transcribed promoters of the ilvYC operon of Escherichia coli is proportional to promoter strengths and transcript lengths.
abstract: The twin-domain model of Liu and Wang suggested that high levels of DNA supercoiling generated in the region between closely spaced divergently transcribed promoters could serve to couple the activities of these promoters transcriptionally. In this report, we use topoisomer sets of defined superhelical densities as DNA templates in a purified in vitro transcription system to demonstrate transcriptional coupling between the divergently transcribed ilvY and ilvC promoters of the ilvYC operon of Escherichia coli. Current evidence for this type of DNA supercoiling-dependent transcriptional coupling, based largely on the in vivo activities of promoters contained in engineered DNA constructs, suggests that the transcription complex must be physically hindered to generate DNA supercoils and to prevent their diffusion throughout the DNA duplex. However, the in vitro results presented here demonstrate that (i) transcriptional coupling is observed between the divergent promoters of the ilvYC operon in the absence of transcript anchoring; (ii) the magnitude of the negative DNA supercoiling generated in the divergent promoter region is proportional to the sum of the global and transcription-induced superhelicity; and (iii) the magnitude of this transcription-induced superhelicity is proportional to promoter strengths and transcript lengths.
authors: Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine, CA 92697, USA.
authors: M L
authors: ML
authors: Opel
authors: G W
authors: GW
authors: Hatfield
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D050540:Ketol-Acid Reductoisomerase; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D012329:RNA, Bacterial; D012333:RNA, Messenger; D014157:Transcription Factors; C073470:LysR protein, Bacteria; D000429:Alcohol Oxidoreductases; D050540:Ketol-Acid Reductoisomerase