The nucleocapsid (N) protein of SARS-coronavirus (SARS-CoV) is the key protein for the formation of the helical nucleocapsid during virion assembly. The nucleocapsid (N) protein of SARS-CoV enters the host cell together with the viral RNA and interferes with several cellular processes. Some of these processes involve interactions between SARS-CoV N protein and host-cell proteins. It has also been demonstrated that the SARS-CoV N protein can bind to DNA in vitro. These interactions might have a role in the pathology of SARS. The N protein may be of potential value in vaccine development for specific prophylaxis and treatment against SARS.