Figure 1. G-G and G-A base pairs as well as minor and major groove GCGC-quartets.

(a) G-G base pair in N1-carbonyl symmetric geometry. (b) G-A base pair in N1-N7, carbonyl-amino geometry. (c) Minor groove GCGC-quartet. (d) Major groove GCGC-quartet. Coordinates are taken from high-resolution structures of VK34 (PDB ID: 5M1L and 5M2L). Deoxyribose moieties are represented by dR. The guanine residues are coloured blue, adenine red and cytosine orange. Hydrogen and O6 atoms are coloured white and red, respectively.