Figure 1.

Schematic representation of (A) telomeres and subtelomeric regions, tandem nucleotide repeats at chromosomal ends that include a double-stranded region and a 50–300 nucleotide single-stranded guanine rich G-tail. Subtelomers (green) represent regions of genes interspersed within repeat elements and interstitial telomeric sequence (red arrow); (B) shelterin complex, the G-tail folds back into the duplex DNA to form the t-loop; (C) G-quadruplex structure, intramolecular G-quadruplex (left) built from G-quartets that are formed through cyclic Hoogsten hydrogen-bonding arrangement of four guanines with each other with G-tetrad structure on the right. Adapted from [23,24].