Fig. 4

CO1-G4 forms in RNA but not DNA. A G4Hunter and QGRS mapper predicted G4 forming sequence (underlined) present upstream of the pause site in the MT-CO1 gene in adult fibroblast samples. B G4-IP in fibroblasts shows enrichment of G4 at this pause site (n = 4; ***P < 0.01; t-test). C NMR spectra for CO1-G4 sequences in RNA, or DNA, or where the guanines are converted to uracil to prevent G4 formation. NMR chemical shifts in the range of 10–12 ppm indicate Hoogsteen base-pairing during quadruplex formation. D Circular dichroism spectra of RNA or DNA oligos corresponding to sequences in panel B, annealed in different buffer solutions. The pattern with minima at ~ 240 nm and maxima at ~ 260 nm is consistent with a parallel G4, whereas minima at ~ 240 nm with maxima at ~ 275 nm is an unfolded oligonucleotide