Our knowledge about the structure and function of the nonstructural proteins (nsps) encoded by the arterivirus replicase gene has advanced significantly in recent years.The continued characterization of arterivirus nsps has not only corroborated several important functional predictions,but also revealed various novel features of arteriviral replication.For porcine reproductive and respiratory syndrome virus (PRRSV),based on bioinformatics predictions and experimental studies,a processing map for the ppla and pplab replicase polyproteins has been developed.