From RNA hairpins to kisses to pseudoknots.

Formation of RNA hairpins presumably initiate the folding of an RNA into its biologically functional form. The stems of the hairpin loops grow to produce A-form helices interrupted by internal loops and bulges. The loops then interact with metal ions and with other loops and bulges to finish folding the RNA into its native biological state. The three-dimensional structures of several of these secondary and tertiary motifs have been determined by nuclear magnetic resonance.