# From Triads to Tools: A Comprehensive Review of the Expanding Roles of G-Triplex Structures

## TL;DR

This paper reviews the expanding roles of G-triplex DNA structures, their formation, characterization, and potential applications in biotechnology and medicine.

## Contribution

The first comprehensive survey of G-triplex DNA and RNA structures, covering recent advances and their potential applications.

## Key findings

- G-triplex DNA can form from truncated G-quadruplex sequences and specifically designed sequences.
- G-triplex structures show promise in biosensing applications compared to G-quadruplex-based systems.
- Protein recognition and effects on DNA replication suggest potential biological relevance of G-triplexes.

## Abstract

Interest in non-canonical DNA structures continues to grow, in part fueled by the recent discovery of a new structure, G-triplex DNA. Originally proposed as folding intermediates for G-quadruplex DNA, G-triplex DNA has more recently been shown to form from truncated G-quadruplex sequence oligonucleotides and other, specifically designed sequences. In this review, we provide the first, comprehensive survey of G-triplex DNA and RNA, covering the literature up to 2024. We include reports of G-triplex DNA from bulk solution and single-molecule approaches, the structural characterization of G-triplex DNA, and the breadth of oligonucleotide sequences that have been reported to form these structures. The formation of G-triplex RNA structures is also reviewed. The evolving understanding of sequence and environmental effects on G-triplex formation are presented together with challenges due to structural polymorphism and competing formation of multimeric G-quadruplex structures. Hints of the biological relevance of G-triplexes are provided by reports of protein recognition of these structures and their effects on DNA replication in vitro. Interaction of G-triplex DNA with a variety of ligands has been reported, although the search for selective ligands that can distinguish G-triplex from G-quadruplex is on-going. The vast majority of publications in the area have focused on the utilization of G-triplex in biosensing applications, which has shown some advantages compared to G-quadruplex-based systems. These results highlight the potential utility of G-triplex structures in a variety of domains and show its promise in applications in biotechnology, medicine, and research.