Severe acute respiratory syndrome (SARS) is a viral respiratory illness caused by a coronavirus called SARS-associated coronavirus (SARS-CoV). SARS coronavirus belongs to a family of enveloped coronaviruses. Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses that belong to the subfamily Coronavirinae. The coronavirus genome encodes a spike protein (S), an envelope protein, a membrane protein, and a nucleoprotein in this order. Nucleoprotein packages the positive strand viral genome RNA into a helical ribonucleocapsid (RNP) and plays a fundamental role during virion assembly through its interactions with the viral genome and membrane protein M. It also plays an important role in enhancing the efficiency of subgenomic viral RNA transcription as well as viral replication.