The molecular biology of SARS coronavirus

Severe acute respiratory syndrome (SARS) is the first emerging infectious disease of the 21st century that has been highly transmissible and fatal and was caused by a previously unknown coronavirus (SARS-CoV). The SARS epidemic in 2003 resulted in more than 8400 SARS cases and approximately 800 deaths. Existing in non-identified animal reservoirs, SARS-CoV continues to represent a threat to humans although more than four years have passed since a large outbreak of SARS, and no new cases have been reported. However, we cannot exclude the possibility of reemergence of SARS. It is hence necessary to understand the biology of the SARS-CoV to deal adequately with the next outbreak, whenever it happens. The SARS-CoV is a novel coronavirus with a large (∼30 thousand nucleotides) positive-sense, single-stranded RNA containing 14 functional open reading frames (ORFs) of which 2 large ORFs constitute the replicase gene which encodes proteins required for viral RNA syntheses. The remaining 12 ORFs encode the 4 structural proteins: spike, membrane, nucleocapsid and envelope; and eight accessory proteins. The viral genome and its expression within the host cell undergoes extensive translational and enzymatic processing to form the 4 structural, 8 accessory and 16 nonstructural proteins. In an effort to understand the molecular mechanisms or capsid assembly and viral pathogenesis, laboratories around the world have adopted a variety of approaches to answering these trivial questions. It has been our effort to consolidate all information known to date about the molecular mechanisms of the SARS-CoV into this chapter to update our readership on the current status of research.