Table 1. K_d (nM) of RIG-I to RNA from NS1.

NS1-vRNA	5′-PPP	capped
3′-UTR (27 nt)	90±30	160±38
U/A-rich (41 nt)	31±5	119±12
5′-UTR (172 nt)	32±8	73±30

Affinities were measured using a fluorescence polarization assay. Values represent the mean ± standard deviation of at least two independent experiments. The RNA molecules with the lowest affinities (in bold) neither bound RIG-I in vivo (Fig. 6) nor induced IFN expression (Fig. 2).