G-quadruplexes are nucleosome-free regions of DNA, forming a secondary structure quadruplex. This region is histone-free, and so may be involved in allowing the removal of nucleosomes from the transcription initiation site. The removal of G-quadruplexes results in a reduction in transcriptional activity.
OGREs, or origin G-rich repeated elements, are G-rich octamers found at many origins of replication. They form the G-quadruplex at the transcription start site.
G quadruplexes readily form in vitro, especially during the study of telomeres. They are also able to form on RNA.
As telomeres are G-rich, they have a high presence of G-quadruplexes, helping to maintain the integrity of chromosomes.