Effect of restoring the zinc-binding domain in Nproof GPE--derived viruses on IRF3 degradation. (A) The amino acid substitution N136D was introduced in Npro of vGPE- and vGPE-/T830A; V2475A; A2563V by site-directed mutagenesis. (B) Swine kidney cells SK-L were inoculated at an MOI of 1 TCID50 per cell with the parent and mutant viruses as indicated. The concentration of the SDS polyacrylamide gels was 7.5%. Proteins were detected at 96 hpi by Western blotting analysis using the anti-porcine IRF3 mAb.