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

r genome organization, they might have acquired these accessory genes from several RNA recombination events with different hosts or viral sources. It is observed that the accessory ORFs are group-specific but are usually truncated to a different extent within a subgroup (Figure 1 ). Another interesting observation is the genetic diversity at the S-E intergenic region. Usually two or three group-specific ORFs are found within this region of each subgroup, but only one confirmed ORF (ORF 3) is found in this region of the SARS-CoV genome (12 -14 , 16 , 22 ) . The diversity (mainly due to truncation and deletion) of these S-E intergenic ORFs within the subgroups is higher than that of other accessory ORFs. Their sequence divergence implies their common ancestors might have acquired these ORFs by RNA recombination, which is a common phenomenon in large RNA viruses (67 , 68 ) , rather than evolved from mutations of a single ancestral RNA sequence segment (9 ) . Typical examples are the acquirement of the HE gene from Influenza C (69 ) and recombination events with Berne virus at the HE-ns2 region (52 ) .