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Description

Single-stranded guanine (G)-rich DNA can form stable secondary structures called G-quadruplexes (G-tetrads or G4). Four guanine bases can associate through Hoogsteen hydrogen bonding to form a square planar structure called a guanine tetrad (G-tetrad), and two or more G-tetrads can stack on top of each other to form a G-quadruplex. The quadruplex structure is further stabilized by the presence of a cation, especially potassium, which sits in a central channel between each pair of tetrads. A DNA G-tetrad can be formed within one DNA strand (intramolecular), between two DNA strands (bimolecular), or four DNA strands (tetramolecular). G4 DNA can arise anywhere in the genome where sufficiently long stretches of single-stranded G-rich DNA are exposed during replication, transcription or recombination. Chemical analysis of quadruplex-forming oligonucleotides has revealed the existence of a plethora of dynamic quadruplex structures with varying stabilities. The diverse nature of G4 DNA structures makes it an appealing topic in molecular biomedical research.