Four structural proteins are essential for virion assembly and infection of CoVs. Homotrimers of S proteins make up the spikes on the viral surface and they are responsible for attachment to host receptors. The M protein has three membrane domains and it shapes the virions, promotes membrane curvature, and binds to the nucleocapsid. The E protein plays a role in virus assembly and release, and it involved in viral pathogenesis. The N protein contains two domains, both of which can bind virus RNA genome via different mechanisms. It is reported that N protein can bind to nsp3 protein to help tether the genome to RTC, and package the encapsidated genome into virions. N is also an antagonist of interferon (IFN) and viral encoded repressor of RNA interference, which appears to be beneficial for the viral replication.