G-Quadruplexes at Telomeres: Friend or Foe?

Molecules. 2020 Aug 13;25(16):3686. doi: 10.3390/molecules25163686.


Telomeres are DNA-protein complexes that cap and protect the ends of linear chromosomes. In almost all species, telomeric DNA has a G/C strand bias, and the short tandem repeats of the G-rich strand have the capacity to form into secondary structures in vitro, such as four-stranded G-quadruplexes. This has long prompted speculation that G-quadruplexes play a positive role in telomere biology, resulting in selection for G-rich tandem telomere repeats during evolution. There is some evidence that G-quadruplexes at telomeres may play a protective capping role, at least in yeast, and that they may positively affect telomere maintenance by either the enzyme telomerase or by recombination-based mechanisms. On the other hand, G-quadruplex formation in telomeric DNA, as elsewhere in the genome, can form an impediment to DNA replication and a source of genome instability. This review summarizes recent evidence for the in vivo existence of G-quadruplexes at telomeres, with a focus on human telomeres, and highlights some of the many unanswered questions regarding the location, form, and functions of these structures.

Keywords: G-quadruplex; telomerase; telomere.

Publication types

  • Review

MeSH terms

  • DNA, Single-Stranded / chemistry
  • DNA, Single-Stranded / genetics
  • G-Quadruplexes*
  • Humans
  • Telomere / chemistry*
  • Telomere / genetics*


  • DNA, Single-Stranded