Mechanically controlled DNA extrusion from a palindromic sequence by single molecule micromanipulation

Area of Science:

• Molecular Biophysics
• Nanotechnology
• Genetics

Background:

• DNA structure and mechanics are fundamental to biological processes.
• Understanding DNA's response to mechanical forces is crucial for molecular biology.
• Palindromic DNA sequences can form complex secondary structures like cruciforms.

Purpose of the Study:

• To investigate the formation and control of cruciform DNA structures using magnetic tweezers.
• To explore the relationship between DNA twisting, stretching, and extrusion.
• To precisely measure the pitch of B-DNA in solution.

Main Methods:

• Utilized a magnetic tweezers setup to apply controlled stretching forces and relative linking number (DeltaLk) to DNA.
• Induce cruciform DNA structure formation by negatively twisting DNA at ~1 pN stretching force.
• Monitored DNA extension changes in response to variations in DeltaLk.

Main Results:

• Successfully induced cruciform DNA structure formation in palindromic DNA in the absence of divalent ions.
• Demonstrated direct and reversible control over DNA extrusion by manipulating DeltaLk.
• Observed a linear relationship between DNA extension and DeltaLk, confirming the nanomechanical gear behavior of the branch point.
• Precisely measured the pitch of B-DNA in solution as 3.61 ± 0.03 nm/turn.

Conclusions:

• Cruciform DNA structures can be formed and manipulated using mechanical forces.
• The DNA branch point acts as a nanomechanical gear, linking rotation and translation.
• This method provides a precise way to measure DNA structural parameters like pitch.