Nucleic acid duplex stability: influence of base composition on cation effects.

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Nucleic acid duplex stability is crucial for molecular interactions.
• Understanding the influence of counter-ions is essential for predicting nucleic acid behavior.
• Oligonucleotide thermostability is influenced by buffer conditions and ionic strength.

Purpose of the Study:

• To investigate the impact of counter-ions on nucleic acid duplex stability.
• To develop predictive models for duplex stability (ΔG°37 and Tm) in specific buffer conditions.
• To explore the relationship between cation binding, base composition, and duplex stability.

Main Methods:

• Thermostability assays of DNA-DNA, RNA-RNA, and RNA-DNA duplexes.
• Analysis of linear free energy relationships across different salt concentrations.
• Measurement of cation binding (Δn) using various divalent cations (MgCl2, CaCl2, BaCl2, MnCl2).

Main Results:

• A linear free energy relationship was observed for oligonucleotide duplexes in 1 M and 100 mM NaCl-phosphate buffer.
• Accurate prediction systems for ΔG°37 and Tm were established with low average errors (2.4°C for Tm, 5.7% for ΔG°37).
• Cation binding (-Δn) is sequence-dependent and influenced by base composition, with evidence of competitive binding between Na+ and Mg2+.

Conclusions:

• Predictive models for oligonucleotide duplex stability in 100 mM NaCl-phosphate buffer are reliable.
• Cation binding is sequence-specific, impacting nearest-neighbor parameters and overall duplex stability.
• Understanding counter-ion effects is key to predicting and manipulating nucleic acid structure and function.