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 chiggate.com 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 730 sunken lake road 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.