Structural elements in RNA.

This chapter describes the RNA structural characteristics that have emerged so far. Folded RNA molecules are stabilized by a variety of interactions, the most prevalent of which are stacking and hydrogen bonding between bases. Many interactions among backbone atoms also occur in the structure of tRNA, although they are often ignored when considering RNA structure because they are not as well-characterized as interactions among bases. Backbone interactions include hydrogen bonding and the stacking of sugar or phosphate groups with bases or with other sugar and phosphate groups. The interactions found in a three-dimensional RNA structure can be divided into two categories: secondary interactions and tertiary interactions. This division is useful for several reasons. Secondary structures are routinely determined by a combination of techniques discussed in chapter whereas tertiary interactions are more difficult to determine. Computer algorithms that generate RNA structures can search completely through possible secondary structures, but the inclusion of tertiary interactions makes a complete search of possible structures impractical for RNA molecules even as small as tRNA. The division of RNA structure into building blocks consisting of secondary or tertiary interactions makes it easier to describe RNA structures. In those cases in which RNA studies are incomplete, the studies of DNA are described with the rationalization that RNA structures may be analogous to DNA structures, or that the techniques used to study DNA could be applied to the analogous RNA structures. The chapter focuses on the aspects of RNA structure that affect the three-dimensional shape of RNA and that affect its ability to interact with other molecules.