Submitted on November 11, 2008
Accepted on December 15, 2008

Cytosolic Viral Sensor RIG-I Is a 5'-Triphosphate–Dependent Translocase on Double-Stranded RNA

¹ Institute for Genomic Biology at University of Illinois Urbana Champaign, 1206 W. Gregory Drive, Champaign, IL 61801, USA.
² Center for Integrated Protein Science and Munich Center for Advanced Photonics at the Gene Center, Ludwig-Maximilians-University of Munich, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
³ Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Room 133, Loomis Laboratory, MC 704, 1110 West Green Street, Urbana, IL 61801, USA.; Howard Hughes Medical Institute.
⁴ Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Harlyne J. Norris Cancer Research Tower, 1450 Biggy Street, Los Angeles, CA 90033, USA.; Department of Microbiology and Molecular Genetics and Tumor Virology Division, New England Primate Research Center, Harvard Medical School, 1 Pine Hill Drive, Southborough, MA 01772, USA.; Institute for Clinical and Molecular Virology, Friedrich-Alexander-University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany.
⁵ Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Harlyne J. Norris Cancer Research Tower, 1450 Biggy Street, Los Angeles, CA 90033, USA.; Department of Microbiology and Molecular Genetics and Tumor Virology Division, New England Primate Research Center, Harvard Medical School, 1 Pine Hill Drive, Southborough, MA 01772, USA.
⁶ Institute for Genomic Biology at University of Illinois Urbana Champaign, 1206 W. Gregory Drive, Champaign, IL 61801, USA.; Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Room 133, Loomis Laboratory, MC 704, 1110 West Green Street, Urbana, IL 61801, USA.; Howard Hughes Medical Institute.

^* To whom correspondence should be addressed.
Sua Myong , E-mail: smyong{at}uiuc.edu

RIG-I is a cytosolic multidomain protein that detects viral RNA and elicits an antiviral immune response. Two N-terminal caspase activation and recruitment domains (CARDs) transmit the signal and the regulatory domain prevents signaling in the absence of viral RNA. 5'-triphosphate and double-stranded (ds) RNA are two molecular patterns that enable RIG-I to discriminate pathogenic from self-RNA. However, the function of the ATPase domain that is also required for activity is less clear. Using single-molecule fluorescence assays, we discovered a robust, ATP-powered dsRNA translocation activity of RIG-I. The CARDs dramatically suppress translocation in the absence of 5'-triphosphate, and the activation by 5'-triphosphate triggers RIG-I to translocate preferentially on dsRNA in cis. This functional integration of two RNA molecular patterns may provide a means to specifically sense and counteract replicating viruses.