FIG 3 .

IFN-β promoter activation requires a minimal length of RNA duplex. A549 cells were transfected with an IFN-β-driven firefly luciferase reporter and a plasmid constitutively expressing Renilla luciferase prior to transfection with various RNAs or RNA/DNA hybrids as indicated. Luciferase activity was determined 20 h post-RNA transfection and normalized to Renilla luciferase activity and is reported as the fold increase compared to the level seen with the mock control without RNA. (A) IFN-β activation stimulated by increasing amounts of our reference RNA (20r; 5′ ppp-blunt-ended dsRNA 20 nt in length; 200, 400, and 800 ng). (B to D) IFN-β activation stimulated by 400 ng of various RNA/DNA hybrids as indicated. (E) Interference experiment. A549 cells were transfected with 200 ng (1×) of our reference RNA (20r) and increasing amounts of various hybrids as indicated (0.5 and 1; 2× and 4×). The total amount of RNA transfected was kept constant, with tRNA tested as inactive with the highest concentration (4× = 800 ng). Data are represented as means ± SD (n = 2). Significance: NS, P > 0.05; *, 0.01 ≤ P < 0.05; **, 0.001 ≤ P < 0.01. See also Fig. S3 in the supplemental material.