In genetics, a kissing stem-loop, or kissing stem loop interaction, is formed in ribonucleic acid (RNA) when two bases between two hairpin loops pair. These intra- and intermolecular kissing interactions are important in forming the tertiary or quaternary structure of many RNAs.[2]
RNA kissing interactions, also called loop-loop pseudoknots, occur when the unpaired nucleotides in one hairpin loop, base pair with the unpaired nucleotides in another hairpin loop.[3] When the hairpin loops are located on separate RNA molecules, their intermolecular interaction is called a kissing complex. These interactions generally form between stem-loops. However, stable complexes have been observed containing only two intermolecular Watson–Crick base pairs.[4][5]