Molecular Advances in Severe Acute Respiratory Syndrome-associated Coronavirus (SARS-CoV)

Chow, Ken Yan Ching; Hon, Chung Chau; Hui, Raymond Kin Hi; Wong, Raymond Tsz Yeung; Yip, Chi Wai; Zeng, Fanya; Leung, Frederick Chi Ching

Based on the recombination and truncation events occurring within these intergenic regions, the phylogenetic relationship between the SARS-CoV and other group 3 coronaviruses has been reconstructed (Figure 2) . At least four subgroup common ancestors (♦ in Figure 2 ) have acquired their S-E intergenic ORFs and other group-specific ORFs from several independent RNA recombination events. Moreover, there is a tendency of deletions or truncations of these ORFs when crossing the species barriers within the subgroups, e.g. ORF 4a/b in group 2 (54 -58 ); ORF 3a/b and ORF 7a/b in group 1 (41 , 42 , 47 , 48 , 50 , 70 -72 ) . The deletions of these redundant accessory ORFs are likely to be the result rather than the cause of crossing the host barriers, as coronavirus host range specificity and tropism have been demonstrated, at least in four studies (7 , 73 -75 ) , as determined by the receptorbinding domain of the spike glycoprotein.