All of them are positive-stranded RNA viruses containing a polycistronic genome of ∼30 kb in size, coding for multiple non-structural proteins (ORF1a and ORF1b, processed into multiple nsp proteins) at the 5′-end plus multiple structural (S, E, M, and N) and lineage-specific accessory proteins (such as ORF3a, ORF3b, ORF6, ORF7a, ORF7b, ORF8a, ORF8b, and ORF9b in SARS-CoV) at the 3′-end (Figure 1).