Severe Acute Respiratory Syndrome (SARS), an emerging disease characterized by atypical pneumonia, has recently been attributed to a novel coronavirus (SARS-CoV). SARS is caused by a human coronavirus, which are the major cause of upper respiratory tract illness in humans, such as the common cold. Coronaviruses are positive stranded RNA viruses, featuring the largest viral RNA genomes known to date (27-31 kb). The spike protein is the main surface antigen of the coronavirus. The most prominent protein in the culture supernatants infected with SARS virus is a 46 kDa nucleocapsid protein. This suggests that the nucleocapsid protein is a major immunogen that may be useful for early diagnostics. The nucleocapsid protein of SARS shares little homology with nucleocapsid proteins of other members of the coronavirus family. Nucleocapsid proteins of other coronavirus have been reported to be involved in forming the viral core and also in the packaging and transcription of the viral RNA.

Inside the virion, complexed with the viral RNA. May be associated with cellular membranes where it participates in viral RNA synthesis and virus budding.