Fig. 4.

PRRSV infectious clone for foreign gene expression. A copy of TRS (Black bar) is inserted between ORF1b and ORF2. Two kinds of sg mRNAs are produced from this construction. The GFP or other foreign genes is inserted between the synthetic TRS (Black bar) and the original TRS (Brown bar), and the original TRS leads to generation of mRNA for GFP expression. The inserted TRS drives the synthesis of sg mRNA for ORF2 expression. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)