Fig. 1
From: In vivo dynamics and regulation of DNA G-quadruplex structures in mammals
G4 and G-tetrad structures. A A typical G4 is formed by assembling four G3-tracts (orange) into three G-tetrads, with each G-tetrad stacked on top of another one. The loop sequence (green) connects adjacent G-tracts. Purple circles represent guanosine monophosphate, and blue spheres represent cations. B Four guanines, each from one of the four G3-tracts, are connected by Hoogsteen hydrogen bonds (black dotted line) to form a square planar plane, the G-tetrad