Fig. 2.

The genome organization and polycistronic nature of the EAV genome. The genomic open reading frames (ORFs) are indicated and the names of the corresponding proteins are depicted. The pink boxes represent the body transcription regulatory sequences (TRSs). The nested set of mRNAs that is found in infected cells is depicted below the genome, with RNA1 being identical to the viral genome and sg mRNAs 2–7 being used to express the structural protein genes located in the 3′-proximal quarter of the genome. The light blue box at the 5′ end of each sg mRNA represents the common leader sequence, which is derived from the 5′ end of the genome. With the exception of the bicistronic sg mRNAs 2 and 5, the sg mRNAs are functionally monocistronic. Translation of proteins from sg mRNAs 2 (E and GP2 proteins) and 5 (ORF5a protein and GP5) occurs by leaky scanning of the 5′-proximal end of these sg mRNAs (Firth et al., 2011, Snijder et al., 1999). The ORFs 1a and 1b located at the 5′ end of the genome and are translated into two polyproteins (pp1a and pp1ab) that are further processed into 12–13 nonstructural proteins by three viral proteases (nsps 1, 2, and 4).