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.