Ebola virus VP35 antagonizes PKR activity through its C-terminal interferon inhibitory domain

Ebola virus VP35 contains a C-terminal cluster of basic amino acids required for double-stranded RNA (dsRNA) binding and inhibition of interferon regulatory factor 3 (IRF3). VP35 also blocks protein kinase R (PKR) activation; however, the responsible domain has remained undefined. Here we show that the IRF inhibitory domain of VP35 mediates the inhibition of PKR and enhances the synthesis of coexpressed proteins. In contrast to dsRNA binding and IRF inhibition, alanine substitutions of at least two basic amino acids are required to abrogate PKR inhibition and enhanced protein expression. Moreover, we show that PKR activation is not only blocked but reversed by Ebola virus infection. Ebola virus (EBOV) infections in humans cause severe hem-orrhagic fevers with high mortality rates (21). A strong dereg-ulation of the host immune response is observed in fatal cases and contributes to the manifestation of symptoms (16). The multifunctional EBOV protein VP35 serves as a polymerase cofactor essential for transcription and replication (18) and as a structural component for virus assembly (9). In addition, it contributes to filoviral immune modulation by impairing th