To determine whether catalytic activity is required for TGEV PL1-mediated inhibition of IFN-β expression, HEK293T cells were cotransfected with alanine mutants of three conserved catalytic residues of TGEV PL1 (C32A, H183A, and D196A) with or without RIG-1, MAVS, STING, or TBK-1, and IFN-β-Luc and pRL-TK plasmids, followed by infection with SeV to activate IFN-β promoter activity. Here, TKT is linked to infection.