Figure 1.

Examples of direct evidence for formation of G-quadruplexes at telomeres. (a) Immunofluorescence of a Stylonychia lemnae cell using an antibody raised against telomeric G-quadruplexes (green). DNA is counterstained in red; the replication band is the unstained region extending across the cell. Image from [35]. (b) Autoradiograph of metaphase spread of human T98G cells cultured with labeled G4 ligand ³H-360A for 48 h. Black arrows indicate silver grains on the terminal regions and red arrows indicate silver grains on the interstitial regions. Bar = 10 µm. Image from [36]. (c) Pull-down of telomeric DNA from human HT1080 cells using the indicated concentrations of a derivative of G4 ligand pyridostatin attached to an affinity tag (2). Genomic DNA was sheared into 100–300 bp pieces prior to pulldown, and telomeric sequences detected by PCR amplification. Reprinted by permission from Springer Nature [37]. (d) Immunofluorescence of a human 293T cell using the BG4 antibody against G-quadruplexes (green) together with fluorescence in situ hybridization against telomeric DNA (red). Arrows indicate G4-telomere colocalizations. Image by A.L. Moye and T.M. Bryan.