G-quadruplexes are four-stranded DNA structures formed by guanine-rich sequences. They are found in telomeres and other regions of the genome, with their function in gene regulation being a topic of recent interest. This study shows that promoter regions of human genes are significantly enriched in G-quadruplex motifs, with over 40% of human gene promoters containing one or more quadruplex motif. These promoter quadruplexes are strongly associated with nuclease hypersensitive sites, which are regions of the genome that are accessible and may be involved in transcription. The study also shows that quadruplex motifs in promoter regions are more stable and show a structural bias towards more stable forms. These findings support the hypothesis that promoter G-quadruplexes are directly involved in the regulation of gene expression. The study used computational methods to map quadruplex motifs in gene promoters and found that they are highly prevalent in human gene promoters. The analysis revealed evidence of evolutionary selection pressure to concentrate quadruplex elements in gene promoters and proximal to the transcription start sites (TSSs) of genes. Promoter quadruplexes were also found to be strongly associated with the open form of chromatinized DNA as judged by experimental genome-wide nuclease hypersensitivity data. The study also found that quadruplex motifs are enriched in regions that are both nuclease hypersensitive and within promoters, showing a remarkable 230-fold enrichment compared to the rest of the genome. These findings suggest that G-quadruplexes may play an important role in gene regulation throughout the genome. The study also shows that the length of the loops between G tracts directly controls the folded geometry and thermodynamic stability of quadruplexes. The presence of single-nucleotide loops is likely to increase the thermal stability of the folded quadruplex structure, a feature likely to be linked to biological function. The study also found that promoter quadruplexes show an enrichment of stabilizing loops that promote a defined fold. These findings support the proposal that quadruplex elements may be cis-acting regulatory elements for a large proportion (40%) of the genes in the human genome. The study also used experimental techniques such as UV melting and circular dichroism to confirm the formation of G-quadruplexes in the promoter regions of genes. The results showed that the sequences studied showed a peak at 260 nm (parallel), and many also showed some amount of peak at 295 nm, suggesting partial formation of anti-parallel structures. These findings support the hypothesis that G-quadruplexes may play an important role in gene regulation throughout the genome. This also opens up opportunities for novel chemical intervention strategies, especially given recent developments in small molecules that target the G-quadruplex structural motif.G-quadruplexes are four-stranded DNA structures formed by guanine-rich sequences. They are found in telomeres and other regions of the genome, with their function in gene regulation being a topic of recent interest. This study shows that promoter regions of human genes are significantly enriched in G-quadruplex motifs, with over 40% of human gene promoters containing one or more quadruplex motif. These promoter quadruplexes are strongly associated with nuclease hypersensitive sites, which are regions of the genome that are accessible and may be involved in transcription. The study also shows that quadruplex motifs in promoter regions are more stable and show a structural bias towards more stable forms. These findings support the hypothesis that promoter G-quadruplexes are directly involved in the regulation of gene expression. The study used computational methods to map quadruplex motifs in gene promoters and found that they are highly prevalent in human gene promoters. The analysis revealed evidence of evolutionary selection pressure to concentrate quadruplex elements in gene promoters and proximal to the transcription start sites (TSSs) of genes. Promoter quadruplexes were also found to be strongly associated with the open form of chromatinized DNA as judged by experimental genome-wide nuclease hypersensitivity data. The study also found that quadruplex motifs are enriched in regions that are both nuclease hypersensitive and within promoters, showing a remarkable 230-fold enrichment compared to the rest of the genome. These findings suggest that G-quadruplexes may play an important role in gene regulation throughout the genome. The study also shows that the length of the loops between G tracts directly controls the folded geometry and thermodynamic stability of quadruplexes. The presence of single-nucleotide loops is likely to increase the thermal stability of the folded quadruplex structure, a feature likely to be linked to biological function. The study also found that promoter quadruplexes show an enrichment of stabilizing loops that promote a defined fold. These findings support the proposal that quadruplex elements may be cis-acting regulatory elements for a large proportion (40%) of the genes in the human genome. The study also used experimental techniques such as UV melting and circular dichroism to confirm the formation of G-quadruplexes in the promoter regions of genes. The results showed that the sequences studied showed a peak at 260 nm (parallel), and many also showed some amount of peak at 295 nm, suggesting partial formation of anti-parallel structures. These findings support the hypothesis that G-quadruplexes may play an important role in gene regulation throughout the genome. This also opens up opportunities for novel chemical intervention strategies, especially given recent developments in small molecules that target the G-quadruplex structural motif.