Figure 1. (A) Three possible structures formed by bulged-out G -hairpins in nearby molecules.

(B) Structure of the hydrogen-bonded G-quartets. Reprinted from Marco-Haviv et al. (1999). DNA molecules can drive the assembly of other DNA molecules into specific four-stranded structures. (Reprinted from J. Mol. Biol.286, 45–56, with permission from the American Chemistry Society.)