In vitro RNA-binding by P19 and P19 mutants. Gel shift assays were performed for FLAG-P19 and mutated FLAG-P19 proteins. A) Increasing amount of FLAG-P19 was incubated for 30 minutes with 0.2 μM si-Fluc at 25°C. The amount of FLAG-P19 were quantified by Western blot analysis using anti-FLAG antibody. B) Equal amounts of purified FLAG-P19 or mutants were incubated for 30 minutes with 0.2 μM si-Fluc at 25°C. RNA was separated on 2% TBE-agarose gel and visualized by staining with ethidium bromide. The protein expression of FLAG-P19 and mutants were shown using Western blot analysis.