Fig. 1.

Transcription and translation of PRRSV genome. (A) PRRSV genome organization. PRRSV possesses a single-stranded positive-sense RNA genome of 15 kb in length with a 3′-polyadenylated tail and the 5′-cap (gray). The viral genome is polycistronic, harboring ORF1a and ORF1b, and structural genes of ORF2a, ORF2b, and ORFs 3 through 7, plus ORF5a within ORF5. (B) Viral gene expression. Non-structural proteins (black) are produced from pp1a and pp1ab after proteolytic processing. The PRRSV replicase-processing scheme involves the rapid auto-proteolytic release of nsp1α, nsp1β, and nsp2 (yellow boxes), mediated by papain-like proteinase (PLP) domains residing in each of them. The remaining polyproteins are processed by nsp4, resulting in a set of 14 individual nsps. The cleavage sites by PLPs and nsp4 are annotated by curved arrows and blue triangles, respectively. Structural proteins (color-coded) are expressed from the subset of sg mRNA. The 3′-co-terminal nested set of minus-strand RNAs is produced as a template for plus-strand sg mRNA synthesis. TRS, transcription regulatory sequence. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)