SARS-CoV-2 N protein restricts IRF3 phosphorylation and nuclear translocation. (A) HEK293T cells were transfected with pFlag-IRF3 or pHA-N or co-transfected with pFlag-IRF3 and pHA-N for 24 h and infected with SeV (MOI = 0.1) for 16 h. The sub-cellular localizations of Flag-IRF3 (red), HA-N (green), and nucleus marker DAPI (blue) were analyzed by confocal microscopy. (B) HEK293T cells were transfected with pHA-N for 24 h and treated with poly(I:C) (2 μg/mL) for 16 h. IRF3 in the nuclear fractions or the cytoplasmic was determined by immunoblotting analyses. GAPDH served as a cytoplasmic control and Lamin A/C served as a nuclear protein control. (C,D) HEK293T cells were transfected with pHA-N for 24 h and (C) infected with SeV (MOI = 0.1) for 16 h, (D) treated with poly(I:C) (2 μg/mL) for 16 h. Phosphorylated IRF3, total IRF3, and GAPDH were subjected to Western blotting with the indicated antibodies anti-pIRF3, anti-IRF3, anti-HA, and anti-GAPDH, respectively.