title: DNA melting and promoter clearance by eukaryotic RNA polymerase I.
abstract: Ribosomal RNA transcription initiation requires the melting of DNA to form an open complex, formation of the first few phosphodiester bonds, commencement of RNA polymerase I movement along the DNA, clearance of the promoter, and the formation of a steady-state ternary elongation complex. We examined DNA melting and promoter clearance by using potassium permanganate, diethylpyrocarbonate and methidiumpropylEDTA.Fe(II) footprinting. In combination, these methods demonstrated: (1) TIF-IB and RNA polymerase I are the only proteins required for formation of an initial approximately 9 base-pair open promoter region. This finding contradicts earlier results using diethylpyrocarbonate alone, which suggested an RNA synthesis requirement for stable melting. (2) DNA melting is temperature-dependent, with a tm between 15 and 20 degrees C. (3) Temperature-dependency of melting, as well as stalling the polymerase at sites close to the transcription start site revealed that the melted DNA region initially opens upstream of the transcription initiation site, and enlarges in a downstream direction coordinate with initiation, eventually attaining a steady-state transcription bubble of approximately 19 base-pairs. (4) The RNA-DNA hybrid protects the template DNA from single-strand footprinting reagents. The hybrid is 9 bp in length, consistent with the longer hybrid estimated by some for the Escherichia coli polymerase and with the hybrids estimated for eukaryotic polymerases II and III.
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins 80523-1870, USA.
authors.forename: B F
authors.initials: BF
authors.lastname: Kahl
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: M R
authors.initials: MR
authors.lastname: Paule
mesh_terms: D000048:Acanthamoeba / Q000201:enzymology / Q000235:genetics; D000818:Animals; D020029:Base Pairing / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism; D004047:Diethyl Pyrocarbonate / Q000378:metabolism; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D020459:Genes, rRNA / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009691:Nucleic Acid Denaturation / Q000235:genetics*; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics; D035463:Pol1 Transcription Initiation Complex Proteins; D011196:Potassium Permanganate / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012521:Sarcosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013696:Temperature; D013698:Templates, Genetic; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D009692:Nucleic Acid Heteroduplexes; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D014157:Transcription Factors; C038200:methidiumpropyl-EDTA-iron(II); C063660:transcription initiation factor TIF-IB; D011196:Potassium Permanganate; C025231:sarkosyl; D004247:DNA; D004492:Edetic Acid; D012318:RNA Polymerase I; D004047:Diethyl Pyrocarbonate; D012521:Sarcosine