Figure 7.

Sequence model for tetrameric G-quadruplexes. (A) Effect of transplanting mutations that induce tetramer formation when present in the central tetrad of the reference construct to the 5′ tetrad (nucleotides 1, 5, 10 and 14) or the 3′ tetrad (nucleotides 3, 7, 12 and 16). Colors match those in Figure 5. (B) Native gel and graph showing effects of point mutations in loops on tetramer formation. (C) Native gel and graph showing the ability of 10 randomly chosen sequences with up to two mutations in loops to form tetramers. Sequences are given in Supplementary Table S1. (D) Loop requirements of G-quadruplex variants that form tetramers. Numbers indicate the positions of loops in the reference construct, and letters below indicate the nucleotides that can occur at each position. Experiments were performed at 10 μM DNA concentration in a buffer containing 200 mM KCl, 1 mM MgCl₂ and 20 mM HEPES pH 7.1. H = A, C or T. Mutations in panels B and C were made in the context of a construct with a GGAG mutation in the central tetrad of the reference construct with the sequence GGGTGGGAAGAGTGGGA.