EMERGING THEMES IN RNA FOLDING

RNAs, like proteins, readily form specific structures adapted for liga nd binding and catalysis. Since they are composed of completely differ ent chemical building blocks, however, RNAs and proteins necessarily u se distinct strategies to assemble complex architectures. While burial of hydrophobic residues drives protein folding, the hydrophobic effec t in RNA contributes primarily to the formation of secondary structure . To form tertiary structure, RNA must overcome electrostatic repulsio ns from the phosphate backbone. How do negatively charged double helic es pack together to produce catalytic centers and ligand binding surfa ces? Here, we review our understanding of the principles that underlie RNA folding based on the structural information currently available.