title: Vaccinia virus RNA helicase: an essential enzyme related to the DE-H family of RNA-dependent NTPases.
abstract: Three distinct nucleic acid-dependent ATPases are packaged within infectious vaccinia virus particles; one of these enzymes (nucleoside triphosphate phosphohydrolase II or NPH-II) is activated by single-stranded RNA. Purified NPH-II is now shown to be an NTP-dependent RNA helicase. RNA unwinding requires a divalent cation and any one of the eight common ribo- or deoxyribonucleoside triphosphates. The enzyme acts catalytically to displace an estimated 10-fold molar excess of duplex RNA under in vitro reaction conditions. NPH-II binds to single-stranded RNA. Turnover of the bound enzyme is stimulated by and coupled to hydrolysis of NTP. Photocrosslinking of radiolabeled RNA to NPH-II results in label transfer to a single 73-kDa polypeptide. The sedimentation properties of the helicase are consistent with NPH-II being a monomer of this protein. Immunoblotting experiments identify NPH-II as the product of the vaccinia virus I8 gene. The I8-encoded protein displays extensive sequence similarity to members of the DE-H family of RNA-dependent NTPases. Mutations in the NPH-II gene [Fathi, Z. & Condit, R.C. (1991) Virology 181, 258-272] define the vaccinia helicase as essential for virus replication in vivo. Encapsidation of NPH-II in the virus particle suggests a role for the enzyme in synthesis of early messenger RNAs by the virion-associated transcription machinery.
authors.affiliation: Program in Molecular Biology, Sloan-Kettering Institute, New York, NY 10021.
authors.forename: S
authors.initials: S
authors.lastname: Shuman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002846:Chromatography, Affinity; D002848:Chromatography, DEAE-Cellulose; D002852:Chromatography, Ion Exchange; D005814:Genes, Viral; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D043583:Nucleoside-Triphosphatase; D016366:Open Reading Frames; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013997:Time Factors; D014616:Vaccinia virus / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D014771:Virion / Q000201:enzymology / Q000254:growth & development
chemical_list: D012330:RNA, Double-Stranded; D012316:RNA Nucleotidyltransferases; D010744:Phosphoric Monoester Hydrolases; D043583:Nucleoside-Triphosphatase; D020365:RNA Helicases