FIG 1.

G quadruplexes. (A) Genetic factors stabilizing G quadruplexes. The general consensus is shown (G3 Nx G3 Nx G3 Nx), with the positions of the two lateral loops and the central loop. A stable G4 structure is formed in the presence of potassium ions if the central loop is shorter than 5 nucleotides and if lateral loops are made of one or two pyrimidine residues. If loops are longer or made of adenine residues, the G4 structure is less stable. The helicase Pif1 is known to unwind G4 in S. cerevisiae (29). (B) Stabilization of the Pu24T quadruplex by PhenDC3. Top view of the top guanine tetrad showing non-Watson-Crick bounds as orange dashed lines. Addition of PhenDC3 stabilizes the structure by stacking with the G4. (Based on data from reference 40.)