title: A conserved motif in region v of the large polymerase proteins of nonsegmented negative-sense RNA viruses that is essential for mRNA capping.
abstract: Nonsegmented negative-sense (NNS) RNA viruses cap their mRNA by an unconventional mechanism. Specifically, 5' monophosphate mRNA is transferred to GDP derived from GTP through a reaction that involves a covalent intermediate between the large polymerase protein L and mRNA. This polyribonucleotidyltransferase activity contrasts with all other capping reactions, which are catalyzed by an RNA triphosphatase and guanylyltransferase. In these reactions, a 5' diphosphate mRNA is capped by transfer of GMP via a covalent enzyme-GMP intermediate. RNA guanylyltransferases typically have a KxDG motif in which the lysine forms this covalent intermediate. Consistent with the distinct mechanism of capping employed by NNS RNA viruses, such a motif is absent from L. To determine the residues of L protein required for capping, we reconstituted the capping reaction of the prototype NNS RNA virus, vesicular stomatitis virus, from highly purified components. Using a panel of L proteins with single-amino-acid substitutions to residues universally conserved among NNS RNA virus L proteins, we define a new motif, GxxT[n]HR, present within conserved region V of L protein that is essential for this unconventional mechanism of mRNA cap formation.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115, USA.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Li
authors.forename: Amal
authors.initials: A
authors.lastname: Rahmeh
authors.forename: Marco
authors.initials: M
authors.lastname: Morelli
authors.forename: Sean P J
authors.initials: SP
authors.lastname: Whelan
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D017124:Conserved Sequence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012315:RNA Caps / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics / Q000378:metabolism*; D018116:Vesiculovirus / Q000235:genetics / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D012315:RNA Caps; D014764:Viral Proteins; C040530:L protein, vesicular stomatitis virus; D012324:RNA-Dependent RNA Polymerase