title: A second, non-canonical RNA-dependent RNA polymerase in SARS coronavirus.
abstract: In (+) RNA coronaviruses, replication and transcription of the giant approximately 30 kb genome to produce genome- and subgenome-size RNAs of both polarities are mediated by a cognate membrane-bound enzymatic complex. Its RNA-dependent RNA polymerase (RdRp) activity appears to be supplied by non-structural protein 12 (nsp12) that includes an RdRp domain conserved in all RNA viruses. Using SARS coronavirus, we now show that coronaviruses uniquely encode a second RdRp residing in nsp8. This protein strongly prefers the internal 5'-(G/U)CC-3' trinucleotides on RNA templates to initiate the synthesis of complementary oligonucleotides of <6 residues in a reaction whose fidelity is relatively low. Distant structural homology between the C-terminal domain of nsp8 and the catalytic palm subdomain of RdRps of RNA viruses suggests a common origin of the two coronavirus RdRps, which however may have evolved different sets of catalytic residues. A parallel between the nsp8 RdRp and cellular DNA-dependent RNA primases is drawn to propose that the nsp8 RdRp produces primers utilized by the primer-dependent nsp12 RdRp.
authors.affiliation: Centre National de la Recherche Scientifique and Universités d'Aix-Marseille I et II, UMR 6098, Architecture et Fonction des Macromolécules Biologiques, Ecole Supérieure d'Ingénieurs de Luminy-Case 925, Marseille Cedex, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Imbert
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Guillemot
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Bourhis
authors.forename: Cécile
authors.initials: C
authors.lastname: Bussetta
authors.forename: Bruno
authors.initials: B
authors.lastname: Coutard
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Egloff
authors.forename: François
authors.initials: F
authors.lastname: Ferron
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Gorbalenya
authors.forename: Bruno
authors.initials: B
authors.lastname: Canard
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary / Q000235:genetics; D012367:RNA, Viral / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D012324:RNA-Dependent RNA Polymerase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D045473:Severe acute respiratory syndrome-related coronavirus / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D012367:RNA, Viral; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase