The interferon inhibitory domain (IID) of EBOV VP35 binds to the endogenous double stranded RNA binding protein 76 (DRBP76) in the presence of dsRNA. A, Experimental outline of MBP-VP35-IID pull down. B, Recombinant MBP or MBP fused to wild-type or mutant VP35 IID was incubated overnight with NP40 buffer or 293T cell lysate in the presence (+) or absence (−) of pIC. Unique bands (labeled 1, 2, and 3) were excised and analyzed by mass spectrometry. Results from the protein database search indicated that protein bands 1, 2, and 3 corresponded to RNA Helicase A, nucleolin, and DRBP76 (also known at NFAR-1 and NF90), respectively. C, Primary sequence of the DRBP76 isoform described previously [26]. The underlined regions indicate the enzymatically digested peptides identified by tandem mass spectrometry. The bold-italic region represents the peptide sequence used to generate a DRBP76 specific antibody used in (D) that is common to 2 of the 6 isoforms. D, Western blot analysis from the same material used in (B) probed with an anti-DRBP76 antibody.