RNA in motion.

Although RNA duplex regions are highly structured and inflexible, other elements of an RNA molecule are capable of dynamic motions. These flexible regions are the sites of interactions with small molecules, proteins, and other RNAs, yet there are few descriptions of these regions that include the timescale and amplitude of their motions. No one technique is sufficient to accurately describe these motions, but the combination of in vitro methods, particularly NMR relaxation methods, and more robust in silico methods, is beginning to yield the type of data that can be used to understand RNA function. Very few RNAs have been described by both techniques, and here one such RNA and one RNA:protein complex are reviewed.