X-ray diffraction from DNA fibres under tension.

Area of Science:

• Biophysics
• Polymer Science
• Structural Biology

Background:

• DNA fibers undergo conformational changes when subjected to mechanical stress, such as stretching during drying.
• Understanding these structural transitions is crucial for comprehending DNA mechanics and its behavior in biological systems.

Purpose of the Study:

• To quantitatively analyze the structural changes in DNA fibers during drying using X-ray diffraction.
• To determine the molecular arrangement and packing within stretched DNA fibers at varying relative humidities.

Main Methods:

• X-ray diffraction studies were performed on stretched DNA fibers.
• Fibers were maintained at different ambient relative humidities to observe structural responses.
• Diffraction patterns were analyzed to determine lattice parameters and molecular arrangements.

Main Results:

• DNA molecules form crystalline arrays when projected down the fiber axis.
• A hexagonal unit cell with a lattice parameter (a) of approximately 13 Å was identified, which changes with humidity.
• Specific X-ray diffraction intensities were observed, including meridional intensities at 1/3.4 Å⁻¹ and 1/6.5 Å⁻¹, an off-meridional intensity at Z=1/5.6 Å⁻¹, and diffuse scatter at Z=1/28 Å⁻¹.

Conclusions:

• The study provides quantitative insights into the structural transitions of DNA fibers under mechanical stress and varying humidity.
• The observed crystalline packing in hexagonal cells highlights the ordered nature of DNA molecules in stretched fibers.
• The identified diffraction features offer a detailed structural fingerprint for DNA fibers, aiding further biophysical investigations.