Schematic illustrations of (a) SARS coronavirus; and (b) The RNA genome of SARS coronavirus containing a 5’-untranslated region, 3’-untranslated region and open reading frames (ORF). ORF1a/b encode non-structure proteins (nsp) and other sequences encode the spike protein (S), envelope protein (E), membrane protein (M), nucleocapsid protein (N) and several accessory proteins (in black). The viral polyproteins (pp1a and pp1ab) translated from ORF1a/b are site-specifically cleaved by the viral Mpro (nsp5, red arrows) and PLpro (nsp3, black arrows) to give viral non-structure proteins.