Fig. (3) NS5A increases the affinity for RNA template binding of the NS5B-WT but not NS5B-D8 mutant. NS5A (2.6 pM) was incubated with NS5B WT (0.9 µM) or NS5B D8 (0.2 µM), then labeled LTMOA RNA was added to 0.2 µM and the reaction was incubated for 0, 2, 10, 20, 30 or 60 min. Samples were examined in a filter binding assay. To quantify, the labeled RNA retained on the membrane was compared to a standard of known RNA concentration.