K-turn motifs in spatial RNA coding.

Three-dimensional architectural motifs are increasingly recognized as determinants of RNA functionality. We submit that such motifs can encode spatial information. RNAs are targeted to subcellular localities in many eukaryotic cell types, and especially in neuronal and glial cells, RNAs can be transported over long distances to their final destination sites. Such RNAs contain cis-acting long-range targeting elements, and recent evidence suggests that kink-turn motifs within such elements may act as spatial codes to direct transport. Kink-turns are complex RNA motifs that feature double- and single-stranded components and introduce a signature three-dimensional structure into helical stems. We propose that the overall architectural design as well as the individual character--as specified by nucleotide identity and arrangement--of kink-turn motifs can serve as RNA targeting determinants.