Recombinant Severe Acute Respiratory Syndrome (SARS) Coronavirus Nucleocapsid Protein Forms a Dimer through Its C-terminal Domain

The causative agent of severe acute respiratory syndrome (SARS) is the SARS-associated coronavirus, SARS-CoV. The viral nucleocapsid (N) protein plays an essential role in viral RNA packaging. In this study, recombinant SARS-CoV N protein was shown to be dimeric by analytical ultracentrifugation, size exclusion chromatography coupled with light scattering, and chemical cross-linking. Dimeric N proteins self-associate into tetramers and higher molecular weight oligomers at high concentrations. The dimerization domain of N was mapped through studies of the oligomeric states of several truncated mutants. Although mutants consisting of residues 1–210 and 1–284 fold as monomers, constructs consisting of residues 211–422 and 285–422 efficiently form dimers. When in excess, the truncated construct 285–422 inhibits the homodimerization of full-length N protein by forming a heterodimer with the full-length N protein. These results suggest that the N protein oligomerization involves the C-terminal residues 285–422, and this region is a good target for mutagenic studies to disrupt N protein self-association and virion assembly.