Fig. 1.

Infectivity of PRRSV genomic RNA and generation of PRRSV from full-length infectious cDNA clones. The full-length genomic cDNA is typically placed under the bacteriophage T7 promoter or the eukaryotic cytomegalovirus (CMV) promoter. The full-length cDNA clone placed under the CMV promoter can directly be transfected into cells, where PRRSV genomic RNA is synthesized in vivo and initiates an infection cycle. If the full-length clone is placed under the T7 promoter, RNA needs to be synthesized in vitro which is then transfected into cells. Using the infectious cDNA clone, the PRRSV genome has been manipulated in its DNA form, and the respective mutant PRRSVs have been generated.