Fig. 2.

Genetic engineering of PRRSV infectious cDNA clones. (A) PRRSV infectious cDNA clones have been engineered to mutate amino acids, delete open reading frames, insert foreign sequences, or substitute a gene with the corresponding sequence from other arteriviruses; GFP: green fluorescence protein gene; EAV: equine arteritis virus; LDV: lactate dehydrogenase elevating virus of mouse; TRS: transcription regulatory sequence. (B) The progressive deletions of ORF7 indicate that secondary RNA structures are important for subgenomic (sg) RNA synthesis; GFP: green fluorescent protein expression; sgGFP: subgenomic mRNA for green fluorescent protein gene; sg7: subgenomic mRNA for ORF7; ^***: substitution of the translation initiation codon for ORF7 to a stop codon to suppress ORF7 expression.