Coronavirus nucleocapsid proteins assemble constitutively in high molecular oligomers

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

To determine whether other CoV N proteins have the same characteristic, we analyzed the SARS-CoV N protein. First, recombinant 6xHis-tagged SARS-CoV N protein was incubated with immobilized GST or GST-tagged SARS-CoV N protein. As shown in Fig. 4a , recombinant SARS-CoV N protein specifically bound to GST-SARS-CoV N protein but not GST, confirming that SARS-CoV N protein self-interacts 12, 23, 24, 27, 28 . Subsequently, bacterial extract from E. coli expressing 6xHis-tagged SARS-CoV N protein was applied onto a 5-20% glycerol gradient. The 6xHis-tagged SARS-CoV N protein was mainly detected in the late fractions of the gradient (Fig. 4c and d) . These results showed that the SARS N protein, similarly to the MHV N protein, forms high molecular weight oligomers. Those of SARS-CoV N protein, however, appear to be smaller and this could be due to either the difference in size between SARS-CoV and MHV N proteins (423 amino acids versus 455) or the fact that SARS-CoV N protein forms smaller oligomers.