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. Author manuscript; available in PMC: 2016 Jun 1.
Published in final edited form as: Curr Opin Virol. 2015 May 13;12:91–98. doi: 10.1016/j.coviro.2015.04.004

Fig. 3.

Fig. 3

The role of RIG-IMDA5 filament formation in signaling. (A) Model of filament-induced (i.e. proximity-induced) oligomerization of RIG-IMDA5 2CARDs. For both RIG-I and MDA5, the linker between 2CARD and the helicase domain is long enough to allow oligomerization of 2CARD alongside the filament. (B) The IFN-β promoter activity of wild-type RIG-I or mutants defective for Ub-binding or -conjugation. While Ub-binding and -conjugation are important for RIG-I-mediated signaling in response to 21 bp dsRNA, their importance diminishes with increasing dsRNA length. This suggests that filament formation (on long dsRNA) compensates for the loss of Ub-mediated oligomerization of 2CARD. (C) Synergism between the filament-induced and Ub-mediated (conjugation and binding) mechanisms for stable oligomerization of 2CARD and robust signaling by RIG-I. The relative importance of each of these mechanisms appears dependent on the dsRNA length. Images in (A) and (B) were adopted from Refs. [18, 25].