DNA Compaction and Charge Neutralization Regulated by Divalent Ions in very Low pH Solution

Area of Science:

• Biochemistry
• Molecular Biology
• Physical Chemistry

Background:

• DNA conformation and compaction are influenced by counterion valence.
• Divalent cations can mediate DNA compaction by lowering solution pH.

Purpose of the Study:

• To determine the critical electrophoretic mobility and charge neutralization fraction for DNA compaction.
• To investigate the effect of counterion concentration on DNA compaction induced by divalent cations at low pH.

Main Methods:

• Electrophoretic mobility measurements of DNA in solutions with varying counterions and pH.
• Analysis of DNA charge neutralization fraction associated with compaction.

Main Results:

• A critical electrophoretic mobility of approximately -1.0 × 10⁻⁴ cm² V⁻¹ s⁻¹ was identified for DNA compaction in trivalent and tetravalent counterion solutions.
• This critical mobility corresponds to an 89% neutralized charge fraction of DNA, consistent with divalent cations at low pH.
• DNA compaction by divalent cations at low pH is reversed by increasing counterion concentration.

Conclusions:

• DNA compaction is critically dependent on achieving a specific charge neutralization threshold.
• The findings provide insights into the physical chemistry governing DNA condensation and decondensation.