PubReading [5] G-Quadruplexes at Telomeres: Friend or Foe? - Tracy Bryan - Molecules

<p><strong>Telomeres</strong> are DNA-protein complexes that cap and protect the ends of linear <strong>chromosomes</strong>. 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 <strong>G-quadruplexes</strong>. This has long prompted speculation that G-quadruplexes play a positive role in telomere biology, resulting in selection for <strong>G-rich tandem</strong> telomere repeats during evolution. There is some evidence that G-quadruplexes at telomeres may play a <strong>protective capping</strong> role, at least in yeast, and that they may positively affect telomere maintenance by either the <strong>enzyme</strong> 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 <strong>genome instability</strong>. 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. - <em>Tracy Bryan</em> - doi:10.3390/molecules25163686 - 2020</p>