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PLoS One. 2014 Sep 26;9(9):e108770. doi: 10.1371/journal.pone.0108770. eCollection 2014.

RIG-I self-oligomerization is either dispensable or very transient for signal transduction.

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Centre International de Recherche en Infectiologie, INSERM, U1111, CNRS, UMR5308, Université Lyon 1, ENS Lyon, Lyon, France.
European Molecular Biology Laboratory, Grenoble Outstation, Grenoble Cedex 9, France; Unit of Virus Host-Cell Interactions, UJF-EMBL-CNRS, UMI 3265, Grenoble Cedex 9, France.


Effective host defence against viruses depends on the rapid triggering of innate immunity through the induction of a type I interferon (IFN) response. To this end, microbe-associated molecular patterns are detected by dedicated receptors. Among them, the RIG-I-like receptors RIG-I and MDA5 activate IFN gene expression upon sensing viral RNA in the cytoplasm. While MDA5 forms long filaments in vitro upon activation, RIG-I is believed to oligomerize after RNA binding in order to transduce a signal. Here, we show that in vitro binding of synthetic RNA mimicking that of Mononegavirales (Ebola, rabies and measles viruses) leader sequences to purified RIG-I does not induce RIG-I oligomerization. Furthermore, in cells devoid of endogenous functional RIG-I-like receptors, after activation of exogenous Flag-RIG-I by a 62-mer-5'ppp-dsRNA or by polyinosinic:polycytidylic acid, a dsRNA analogue, or by measles virus infection, anti-Flag immunoprecipitation and specific elution with Flag peptide indicated a monomeric form of RIG-I. Accordingly, when using the Gaussia Luciferase-Based Protein Complementation Assay (PCA), a more sensitive in cellula assay, no RIG-I oligomerization could be detected upon RNA stimulation. Altogether our data indicate that the need for self-oligomerization of RIG-I for signal transduction is either dispensable or very transient.

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