a RAW 264.7 macrophages were transfected with 1 μg ml−1 poly(I:C). Two hours later, cells were harvested and immunoprecipitated with control IgG or the anti-RIG-I antibody. The IP and lysate samples were blotted with the indicated antibodies. Molecular weights (MW) are indicated. b A549 cells were transfected with 1 μg ml−1 poly(I:C). Two hours later, cells were fixed and stained with the anti-FIP200 antibody (green), anti-RIG-I antibody (red), and DAPI (blue). Bar = 10 μm. c A549 cells were transfected with 1 μg ml−1 poly(I:C). Two hours later, cells were fixed, and the proximity ligation assays were performed. ***P < 0.001, by one-way ANOVA, followed by Tukey’s multiple comparison test. d Schematics of the RIG-I mutants. CARD: caspase activation and recruitment domain; CTD: C-terminal domain; Hel-CTD: helicase domain plus CTD. e FLAG-tagged FIP200 (FIP200-FLAG) was transfected with the indicated HA-tagged RIG-I mutants into HEK293 cells. After 48 h, cell lysates were collected, and then immunoprecipitated and blotted as indicated. f Schematics of the FIP200 mutants. UBQ: ubiquitin-like; CC: coiled coil; ATG: ATG11-like. g HA-tagged RIG-I (RIG-I-HA) was transfected with FLAG-tagged FIP200 and the indicated mutants into HEK293 cells. After 48 h, cell lysates were collected, and then immunoprecipitated and blotted as indicated. h His-tagged ATG domain (ATG-His) was mixed with MBP, MBP-tagged CARD1, or CARD2 in vitro at 4 °C for 16 h. Then, MBP pull-down assay was performed and blotted as indicated. All proteins were purified from E. coli. i Schematics of the alpha helix and Claw deletion mutant. j Myc-tagged RIG-I (RIG-I-Myc) was transfected with FLAG-tagged FIP200 and the indicated mutants into HEK293 cells. After 48 h, cell lysates were collected, and then immunoprecipitated and blotted as indicated. k Purified recombinant His-tagged Claw domain of FIP200 (Claw-His) was mixed with GST or GST-tagged 2CARD in vitro at 4 °C for 16 h. Then, His pull-down was performed and blotted as indicated.