Mapping of single-base differences between two DNA strands in a single molecule using holliday junction nanomechanics

Area of Science:

• Molecular Biology
• Biophysics
• Nanotechnology

Background:

• Accurate DNA sequence comparison is crucial for various biological and biotechnological applications.
• Existing methods often require amplification or labeling, limiting direct mechanical analysis.
• Understanding DNA mechanics at the single-molecule level offers new avenues for sequence analysis.

Purpose of the Study:

• To demonstrate a novel single-molecule assay for DNA sequence comparison.
• To utilize DNA mechanics and a Holliday junction as the core mechanism for sequence discrimination.
• To establish a purely mechanical method for detecting sequence differences.

Main Methods:

• Constructed a DNA molecule with two homologous, non-identical sequences forming a Holliday junction.
• Employed magnetic tweezers to apply force and winding, controlling Holliday junction formation and migration.
• Measured construct end-to-end distance to monitor Holliday junction behavior during intra-molecular recombination.

Main Results:

• Holliday junction migration occurred in regions of sequence identity.
• A single-base difference caused a persistent blockage of Holliday junction migration.
• Migration blockages, detected via plectoneme formation, allowed for sequence difference mapping.

Conclusions:

• A novel single-molecule DNA sequence comparison assay based on Holliday junction mechanics was developed.
• The assay uses the Holliday junction as a nanomechanism where mismatches act as migration blockers.
• This mechanically-based approach shows potential for future biotechnology applications.