RNA Triple Helices: From Structures and Mechanisms to Therapeutic Targets.

Major-groove RNA triple helices are conserved tertiary structures formed when a third strand inserts into the major groove of a classic double helix either via Hoogsteen base pairing or reverse Hoogsteen base pairing. These structures are widely distributed in eukaryotic, prokaryotic, and viral RNAs. This paper systematically summarizes the structural classification, stability-influencing factors, and identification methods of RNA triple helices. A growing body of evidence indicates that RNA triple helices are extensively involved in diverse biological processes, including RNA stability regulation, translation regulation, riboswitch ligand recognition, transposition regulation, telomerase activity, and the assembly of the spliceosome catalytic core, as well as serving as scaffolds for molecular recruitment. Notably, dysregulation of RNA triple helices is closely associated with tumorigenesis, viral infections, and genetic diseases. Based on their structural and functional characteristics, multiple therapeutic strategies targeting RNA triple helices have been explored, such as small molecules and antisense oligonucleotides. Collectively, RNA triple helices represent a pivotal link between RNA structural biology and precision medicine, with promising potential as an important candidate target for future RNA structural drug development.