Effects of Length and Loop Composition on Structural Diversity and Similarity of (GTGNGTG) G-Quadruplexes.

A G-rich sequence containing three loops to connect four G-tracts with each ≥2 guanines can possibly form G-quadruplex structures. Given that all G-quadruplex structures comprise the stacking of G-quartets, the loop sequence plays a major role on their folding topology and thermal stability. Here circular dichroism, NMR, and PAGE are used to study the effect of loop length and base composition in the middle loop, and a single base difference in loop 1 and 3 on G-quadruplex formation of (GHGNGHG) sequences with and without flanking nucleotides, where H is T, A, or C and N is T, A, C, or G.