Competitive triplex/quadruplex equilibria involving guanine-rich oligonucleotides

Area of Science:

• Molecular Biology
• Biochemistry
• Oligonucleotide Chemistry

Background:

• Oligonucleotide-directed triple helix formation is a strategy for gene inhibition.
• Guanine-rich oligonucleotides bind to duplex DNA to form these structures.
• Physiological concentrations of monovalent cations, particularly K+, inhibit this process.

Purpose of the Study:

• To elucidate the mechanism by which monovalent cations inhibit triple helix formation.
• To investigate oligonucleotide aggregation under inhibitory cation concentrations.
• To assess the role of guanine quartets in this inhibition.

Main Methods:

• Electrophoretic gel mobility shift titrations were employed.
• Analysis of triplex formation and stability in the presence of monovalent cations (M+).
• Monitoring of oligonucleotide aggregation under varying M+ concentrations.

Main Results:

• Monovalent cation inhibition showed dependence on cation concentration and ionic radius, correlating with guanine quartet stabilization.
• Guanine-rich oligonucleotides formed aggregates resembling guanine quartets in the presence of inhibitory M+.
• K+ inhibition was not reversed by polyamines (spermidine3+, spermine4+).
• M+ reduced triplex formation rate and increased triplex dissociation rate, indicating competing equilibria.

Conclusions:

• Monovalent cations inhibit triple helix formation by promoting guanine-rich oligonucleotide aggregation via guanine quartets.
• This aggregation represents a competing equilibrium that hinders in vivo applications.
• Strategies to destabilize these aggregates are necessary for successful in vivo gene inhibition.