Analysis of severe acute respiratory syndrome coronavirus structural proteins in virus-like particle assembly

SARS-CoV has four major structural proteins: the N, S, M, and E proteins. To investigate the mechanism of SARS-CoV assembly, we cloned the genes encoding these four proteins into the eukaryotic expression vector pCAGGS and transfected them into 293T cells. When all four expression vectors were co-transfected VLP formed, as confirmed using electron microscopy. Using a rabbit polyclonal antibody specific to the N protein, N-protein-containing particles similar in size to the VLP were also observed by immunoelectron microscopy, indicating that the VLP contained the N protein. Co-immunoprecipitation analyses demonstrated an interaction between the N and M proteins, suggesting that N protein binds directly to M protein to be incorporated into VLP.