A new principle of RNA folding based on pseudoknotting.

Tertiary interactions involving hairpin or interior loops of RNA can lead to extended quasi-continuous double helical stem regions, consisting of coaxially stacked segments of duplex RNA, bridged by single-stranded connections. This type of compact folding plays a role in various strategic regions of RNA molecules. Their role in ribosome functioning, RNA splicing and recognition of tRNA-like structures is discussed.