Production of type I interferons is essential for the establishment of anti-viral status and clearance of invading viruses.During infection of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) however,only a low level of IFNs is detected and the disease is often associated with viral persistence.Non-structural protein (nsp) 1 is the first viral protein synthesized during infection and has been reported to be a viral IFN antagonist.Nspl is cleaved into two subunits,nspl-alpha and nspl-beta,and the nspl-alpha subunit has been shown to degrade the CREB-binding protein in the nucleus,resulting in the suppression of IFN production.The present study was conducted to explore the molecular basis of the nsp 1-beta subunit-based IFN modulation.