Antiviral innate immunity relies on the recognition of microbial structures. One such structure is viral RNA that carries a triphosphate group on its 5′ terminus (PPP-RNA). By an affinity proteomics approach with PPP-RNA as the 'bait', we found that the antiviral protein IFIT1 (interferon-induced protein with tetratricopeptide repeats 1) mediated binding of a larger protein complex containing other IFIT family members. IFIT1 bound PPP-RNA with nanomolar affinity and required the arginine at position 187 in a highly charged carboxy-terminal groove of the protein. In the absence of IFIT1, the growth and pathogenicity of viruses containing PPP-RNA was much greater. In contrast, IFIT proteins were dispensable for the clearance of pathogens that did not generate PPP-RNA. On the basis of this specificity and the great abundance of IFIT proteins after infection, we propose that the IFIT complex antagonizes viruses by sequestering specific viral nucleic acids.
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We thank the NIH Knockout Mouse Project for embryonic stem cells with a targeted Ifit1 allele; L. Andersen for population expansion of embryonic stem cells; K. Kandasamy for bioinformatics support; G. Kochs (University of Freiburg) for plasmid Pol-I FF-luc; T. Decker (University of Vienna) for IRF3-deficient MEFs. Supported by the Austrian Academy of Sciences, the European Research Council (G.S.-F.), the European Molecular Biology Organization (C.L.B.; and ATLF 463-2008 to A.P.), the European Union (Marie Curie Fellowship to C.L.B.), Deutsche Forschungsgemeinschaft (We 2616/5-2 and SFB 593/B13 to F.W.), the Austrian Federal Ministry for Science and Genome Research in the Research Austria program Austromouse (T.R. and M.M.), the Bioinformatics Integration Network (J.C.) and the Austrian Science Fund (FWF SFB F28 to M.M.).
The authors declare no competing financial interests.
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Pichlmair, A., Lassnig, C., Eberle, C. et al. IFIT1 is an antiviral protein that recognizes 5′-triphosphate RNA. Nat Immunol 12, 624–630 (2011). https://doi.org/10.1038/ni.2048
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