(A) Electrophoretic mobility shift assay of purified MDA5 incubated with 24 bp RNA for 40 min on ice in the presence or absence of DHX29 protein. (B) AFM images of purified MDA5 protein in the presence and absence of DHX29 protein. (C) Section mode analysis was done to determine the height of the RNA-protein complexes. a, RNA alone (control); b1 and b2, RNA-DHX29; c, RNA-MDA5; and d, MDA5 plus DHX29. Data are plotted as the mean ± s.d. of ten independent site measurements. *P < 0.05, **P <0.01, ***P <0.001 vs. the corresponding control. (D) A proposed working model to illustrate the critical role of DHX29 in the control and activation of MDA5-mediated RNA recognition and type I IFN signaling.