title: Synthesis and characterization of a new photocrosslinking CTP analog and its use in photoaffinity labeling E. coli and T7 RNA polymerases.
abstract: A new photocrosslinking CTP analog that functioned as a substrate during transcription was synthesized and used to photoaffinity label E. coli and bacteriophage T7 RNA polymerases. This analog, 5-((4-azidophenacyl)thio) cytidine-5'-triphosphate (5-APAS-CTP) contains an aryl azide group approximately 10 A from the nucleotide base and specifically replaced CTP during synthesis of RNA by both polymerases. Analog was placed at the 3' end or internally within RNA. Both polymerases inefficiently incorporated two 5-APAS-CMP molecules sequentially, as was found for the related 5-APAS-UMP. Analog was placed at the 3' end of RNA in transcription complexes paused at the site of Q-modification of E. coli RNA polymerase, downstream of the lambda PR' promoter (+16), a pause that requires specific DNA sequences but no apparent RNA hairpin. Crosslinking was examined in the presence and absence of the NusA protein, which enhances the transcriptional pause at this site and is required for Q modification of the polymerase. Crosslinking of the 3' end of the RNA to NusA was not observed, consistent with our earlier results involving a NusA-enhanced pause site downstream from an RNA hairpin.
authors.affiliation: Department of Botany and Microbiology, University of Oklahoma, Norman 73019.
authors.forename: M M
authors.initials: MM
authors.lastname: Hanna
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: J C
authors.initials: JC
authors.lastname: Reidling
authors.forename: M J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: J
authors.initials: J
authors.lastname: Jou
mesh_terms: D000345:Affinity Labels; D001386:Azides / Q000737:chemistry*; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D003432:Cross-Linking Reagents; D003570:Cytidine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D010445:Peptide Elongation Factors; D012313:RNA / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins
chemical_list: D000345:Affinity Labels; D001386:Azides; D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins; C068727:nusA protein, E coli; C081396:5-((4-azidophenacyl)thio)cytidine-5'-triphosphate; D012313:RNA; D003570:Cytidine Triphosphate; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases