title: Discrimination against deoxyribonucleotide substrates by bacterial RNA polymerase.
abstract: Nucleic acid polymerases have evolved elaborate mechanisms that prevent incorporation of the non-cognate substrates, which are distinguished by both the base and the sugar moieties. While the mechanisms of substrate selection have been studied in single-subunit DNA and RNA polymerases (DNAPs and RNAPs, respectively), the determinants of substrate binding in the multisubunit RNAPs are not yet known. Molecular modeling of Thermus thermophilus RNAP-substrate NTP complex identified a conserved beta' subunit Asn(737) residue in the active site that could play an essential role in selection of the substrate ribose. We utilized the Escherichia coli RNAP model system to assess this prediction. Functional in vitro analysis demonstrates that the substitutions of the corresponding beta' Asn(458) residue lead to the loss of discrimination between ribo- and deoxyribonucleotide substrates as well as to defects in RNA chain extension. Thus, in contrast to the mechanism utilized by the single-subunit T7 RNAP where substrate selection commences in the inactive pre-insertion site prior to its delivery to the catalytic center, the bacterial RNAPs likely recognize the sugar moiety in the active (insertion) site.
authors.affiliation: Department of Microbiology, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Svetlov
authors.forename: Dmitry G
authors.initials: DG
authors.lastname: Vassylyev
authors.forename: Irina
authors.initials: I
authors.lastname: Artsimovitch
mesh_terms: D001216:Asparagine / Q000737:chemistry; D001665:Binding Sites; D002241:Carbohydrates / Q000737:chemistry; D020134:Catalytic Domain; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry*; D003854:Deoxyribonucleotides / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D010957:Plasmids / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013379:Substrate Specificity; D016963:Thermus thermophilus / Q000737:chemistry; D014158:Transcription, Genetic; D014764:Viral Proteins
chemical_list: D002241:Carbohydrates; D003854:Deoxyribonucleotides; D012333:RNA, Messenger; D014764:Viral Proteins; D001216:Asparagine; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases