Coronavirus nucleocapsid proteins assemble constitutively in high molecular oligomers

Cong, Yingying; Kriegenburg, Franziska; de Haan, Cornelis A. M.; Reggiori, Fulvio

Previous data have shown that the N2b/CTD domain of SARS-CoV N protein domain self-interacts 24, 26, 31, 34 . To explore whether the N-terminus of the SARS-CoV N protein also participates in its oligomerization, as seen for the MHV N protein, we performed pull-down experiments with recombinant 6xHis-tagged SARS-CoV-N1-N2a and immobilized GST-SARS-CoV-N1-N2a. As depicted in Fig. 4b , recombinant SARS-CoV N1-N2a protein specifically binds to GST-SARS-CoV N1-N2a protein but not GST alone, revealing that the N-terminal N1-N2a domain self-interacts. Moreover, analysis of recombinant 6xHis-tagged SARS-CoV-N1-N2a on glycerol gradients showed that this truncation forms high molecular weight oligomers (Fig. 4d and e) . Similarly to MHV, however, SARS-CoV-N2a was unable to self-interact and form oligomers (Supplementary Fig. S3 ). Altogether our results confirm that the SARS-CoV N protein oligomerizes but the oligomerization process involves not only the CTD domain but also the N-terminal area of the N protein, which contains the NTD domain.