Abstract
Recent discovery of several functional nucleic acids has changed our concept about their roles in biological system, and oppened a new field of RNA world. Except for the Watson-Crick base pairings, non-canonical hydrogen bondings have been found between bases, between base and ribose, and between riboses. They are participated in specific roles for folding the stem parts in the characteristic tertiary structure, and to realize a special function on it. In this article, several structural motifs will be disscussed with some examples.
