Structural motifs in RNA.

An RNA motif is a discrete sequence or combination of base juxtapositions found in naturally occurring RNAs in unexpectedly high abundance. Because all the motifs examined so far have three-dimensional structures independent of the context in which they are embedded, they are important components of the "kit" of structural elements from which RNAs are constructed. This review discusses the structures of the motifs that have been identified so far and speculates on the importance of their role in determining RNA conformation and their evolutionary origin.