Competitive triplex quadruplex equilibria involving guanine-rich oligonucleotides

Electrophoretic gel mobility shift titration studies of oligonucleotide-directed triple helix formation in the purine motif via binding of guanine-rich oligonucleotides to duplex DNA confirm that physiological concentrations of Na+ and K+ inhibit triple helix formation. Competing equilibria, in which guanine-rich oligonucleotides form aggregates involving guanine quartets, lead to triplex inhibition. Physiological polyamines reverse the K+-induced inhibition of triplexes.