@article{179191,
  keywords = {RNA, RNA, Double-Stranded, Protons, Molecular Sequence Data, Mutagenesis, Site-Directed, Amino Acid Sequence, Sequence Homology, Amino Acid, DNA-Directed RNA Polymerases, Viral Proteins, Protein Multimerization, SARS Virus, Amino Acid Motifs, RNA-Dependent RNA Polymerase, Cations, Divalent},
  author = {Aartjan Te Velthuis and van den Sjoerd Worm and Eric Snijder},
  title = {The SARS-coronavirus nsp7+nsp8 complex is a unique multimeric RNA polymerase capable of both de novo initiation and primer extension},
  abstract = { Uniquely among RNA viruses, replication of the ~30-kb SARS-coronavirus genome is believed to involve two RNA-dependent RNA polymerase (RdRp) activities. The first is primer-dependent and associated with the 106-kDa non-structural protein 12 (nsp12), whereas the second is catalysed by the 22-kDa nsp8. This latter enzyme is capable of de novo initiation and has been proposed to operate as a primase. Interestingly, this protein has only been crystallized together with the 10-kDa nsp7, forming a hexadecameric, dsRNA-encircling ring structure [i.e. nsp(7+8), consisting of 8 copies of both nsps]. To better understand the implications of these structural characteristics for nsp8-driven RNA synthesis, we studied the prerequisites for the formation of the nsp(7+8) complex and its polymerase activity. We found that in particular the exposure of nsp8{\textquoteright}s natural N-terminal residue was paramount for both the protein{\textquoteright}s ability to associate with nsp7 and for boosting its RdRp activity. Moreover, this {\textquoteright}improved{\textquoteright} recombinant nsp8 was capable of extending primed RNA templates, a property that had gone unnoticed thus far. The latter activity is, however, ~20-fold weaker than that of the primer-dependent nsp12-RdRp at equal monomer concentrations. Finally, site-directed mutagenesis of conserved D/ExD/E motifs was employed to identify residues crucial for nsp(7+8) RdRp activity. },
  year = {2012},
  journal = {Nucleic Acids Res},
  volume = {40},
  pages = {1737-47},
  month = {02/2012},
  issn = {1362-4962},
  doi = {10.1093/nar/gkr893},
  language = {eng},
}