Figure 1.

2′O-Methylation at N₁ Position of RNA Critically Determines the Abolition of RIG-I Activation

(A) The chemical structure of cap structures as contained in eukaryotes’ mRNA is presented (^m7GpppN_mN_m). Important structural features are labeled. The cap2 structure, which occurs only in higher eukaryotes’ mRNA, consists of a G, 5′-5′ triphosphate linked to N₁, with methylation at N₇ of the G residue. N₁ and N₂ are 2′O-methylated.

(B and C) Chloroquine-treated human PBMCs were stimulated with the indicated synthetic RNA oligonucleotides (see also Table S1 and Figure S2) at concentrations of 2.5 nM and 5 nM (B) or a dose titration was performed (C). Before stimulation, RNA oligonucleotides were hybridized with the complementary RNA (AsGA) to blunt-ended double-stranded RNA. IFN-α production was analyzed 20 hr after stimulation. Data from four donors are depicted as mean values + SEM.

(D) Murine bone-marrow-derived dendritic cells from MDA5- or RIG-I-deficient or wild-type mice were stimulated with indicated RNA ligands (50 nM) and murine IFN-α was determined by ELISA (linear range limit: 80 pg/ml) 20 hr after transfection. One representative experiment out of two is shown. Error bars indicate SD.