Amino acid at position 176 was essential for porcine reproductive and respiratory syndrome virus (PRRSV) non-structural protein 1α (nsp1α) as an inhibitor to the induction of IFN-β.

Previous studies have shown that porcine reproductive and respiratory syndrome virus (PRRSV) nonstructural protein 1α (nsp1α) was the interferon (IFN) antagonist. However, the mechanism was unclear. In the present study, deletion of the carboxyl-terminal extension (CTE) (167-180 amino acid (aa)) made nsp1α lose its inhibitory ability to the induction of IFN-β. And a series of C-terminal truncated mutants for nsp1α showed that 1-176 aa of nsp1α was able to inhibit the induction of IFN-β and deleting or mutating the amino acid F176 made nsp1α not inhibit the induction of IFN-β. In conclusion, the CTE and the amino acid F176 were critical for nsp1α as the IFN antagonist and the region representing 167-176 was the minimal subunit of the CTE for nsp1α to retain its suppressive activity to the induction of IFN-β.