Figure 3.

Cooperative folding of dimeric and tetrameric G-quadruplexes. (A) Native gel showing dimer formation as a function of KCl concentration. (B) Native gel showing dimer formation as a function of MgCl₂ concentration. (C) Graph showing dimer formation as a function of KCl and MgCl₂ concentration. (D) Graph showing tetramer formation as a function of KCl and MgCl₂ concentration. Dimers were generated using a construct with an AGGG mutation in the central tetrad of the reference construct and the sequence GAGTGGGAAGGGTGGGA. Tetramers were generated using a construct with a GGAG mutation in the central tetrad of the reference construct and the sequence GGGTGGGAAGAGTGGGA. Experiments were performed at 1 μM G-quadruplex concentration in a buffer containing 20 mM HEPES pH 7.1 and either 0–1000 mM KCl or 0–20 mM MgCl₂.