A second, non-canonical RNA-dependent RNA polymerase in SARS coronavirus.
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.
Imbert
Isabelle
I
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.
Guillemot
Jean-Claude
JC
Bourhis
Jean-Marie
JM
Bussetta
Cécile
C
Coutard
Bruno
B
Egloff
Marie-Pierre
MP
Ferron
François
F
Gorbalenya
Alexander E
AE
Canard
Bruno
B
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
D012367:RNA, Viral; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase