Fig. 1.

The WNV −1 PRF signal can assume 7 different conformations, 5 of which fold/unfold along the dual stem-loop pathway, while 2 follow the pseudoknot course. The structures along the 2 pathways are mutually incompatible, and the pathways only interconvert through the unfolded state. The tension required to induce ribosome stalling, which allows ribosomes to slide from the incoming reading frame (N NNW WWH) to the −1 frame (NNN WWW H), is in the same range as the force at which the RNA conformational changes occur. The high degree of conformational heterogeneity and complex dynamics are proposed to enable extremely high rates of −1 PRF.