Figure 1.

(A) Different four-repeat human telomeric DNA sequences. WT-Tel26, Tel22 and Tel23 are the wild-type four-repeat telomeric DNA sequences with sizes of 26-, 22- and 23-nt, respectively. Mut-Tel24 is the modified sequence used in the recent report (25). The numbering system is shown above Tel26. (B) The imino proton region of the 1D ¹H NMR spectrum of Tel26 in K⁺ with assignment. (C) Schematic drawing of the folding topology of the unimolecular human telomeric G-quadruplex in K⁺ solution. The three naturally occurring adenine residues involved in the adenine triple capping structure are shown in red. Yellow box = (anti) guanine, orange box = (syn) guanine; green ball = guanine, red ball = adenine, blue ball = thymine.