The cell’s ability to distinguish invading RNA or DNA from the plethora of its own nucleic acid sequences plays a critical role in protecting the genome from potentially harmful damage, and a number of systems have evolved to sniff out unwanted alien genes and trigger cellular responses. Retinoic acid-inducible protein I (RIG-I), part of the cellular alarm system in the cytoplasm, specifically recognizes a number of RNA viruses, but what is RIG-I actually sensing? Hornung et al. and Pichlmair et al. show that RIG-I detects and binds to an unusual feature of the 5′ end of the viral RNA, specifically, a 5′-phosphate group.
V. Hornung, J. Ellegast, S. Kim, K. Brzózka, A. Jung, H. Kato, H. Poeck, S. Akira, K.-K. Conzelmann, M. Schlee, S. Endres, G. Hartmann, 5′-Triphosphate RNA is the ligand for RIG-I. Science 314, 994-997 (2006). [Abstract] [Full Text]
A. Pichlmair, O. Schulz, C. P. Tan, T. I. Näslund, P. Liljeström, F. Weber, C. Reis e Sousa, RIG-I-mediated antiviral responses to single-stranded RNA bearing 5′-phosphates. Science 314, 997-1001 (2006). [Abstract] [Full Text]