doi: 10.1093/nar/gku536 Structural studies of CNG repeats

CNG repeats (where N denotes one of the four natu-ral nucleotides) are abundant in the human genome. Their tendency to undergo expansion can lead to hereditary diseases known as TREDs (trinucleotide repeat expansion disorders). The toxic factor can be protein, if the abnormal gene is expressed, or the gene transcript, or both. The gene transcripts have attracted much attention in the biomedical commu-nity, but their molecular structures have only recently been investigated. Model RNA molecules compris-ing CNG repeats fold into long hairpins whose stems generally conform to an A-type helix, in which the non-canonical N-N pairs are flanked by C-G and G-C pairs. Each homobasic pair is accommodated in the helical context in a unique manner, with con-sequences for the local helical parameters, solvent structure, electrostatic potential and potential to in-teract with ligands. The detailed three-dimensional profiles of RNA CNG repeats can be used in screen-ing of compound libraries for potential therapeutics and in structure-based drug design. Here is a brief survey of the CNG structures published to date