TAX1BP1 inhibits IFNβ activation at the level of TBK1-IKKi. A–C, 293T cells were transfected with IFNβ luc reporter (100 ng) and pRL-tk (10 ng) plasmids together with ΔRig-I (A), ΔMDA5 (B), or IPS-1 (C) (1 μg) and a plasmid expressing TAX1BP1 (1 μg). D, 293T cells were transfected as described in C except an NF-κB luc reporter (100 ng) was used. E–G, 293T cells were transfected as in A–C using plasmids (1 μg each) encoding either TBK1 (E), IKKi (F), or a constitutively active form of IRF3 (IRF3 SA) (G) with or without TAX1BP1 DNA (1 μg). H, 293T cells were transfected with either control (Cont.) scrambled or TAX1BP1 siRNA. After 24 h, cells were transfected with IFNβ luc, pRL-tk, and IKKi plasmids as in F. Error bars, S.E.