Related Experiment Videos
Supercoiled DNA is interwound in liquid crystalline solutions
The EMBO Journal
|December 20, 1989
Summary
Supercoiled DNA forms rod-like particles in liquid crystals, suggesting an interwound structure. Neutron diffraction reveals key parameters for this DNA conformation, supporting the double-helix model.
Area of Science:
- Structural biology
- Biophysics
- Molecular genetics
Background:
- Supercoiled DNA structure is debated, with models including toroidal rings and interwound duplex rods.
- The interwound rod model is common but lacks definitive structural evidence.
Purpose of the Study:
- To investigate the structure of supercoiled DNA in concentrated solutions.
- To determine structural parameters of supercoiled DNA using biophysical techniques.
Main Methods:
- Neutron diffraction of plasmid DNA (pUC8 and pKS414) in liquid crystalline phases.
- X-ray fiber diffraction at high relative humidity.
Main Results:
- Supercoiled plasmids form hexagonally packed, parallel rod-like particles in liquid crystals.
- Mass/unit length is ~3.6x that of linear DNA, implying a superhelical pitch angle of ~36 degrees.
- Deduced supercoil pitch and radius are ~360 Å and ~80 Å, respectively, consistent with a B-form duplex.
Conclusions:
- The rod-like structure supports an interwound conformation for supercoiled DNA.
- Structural parameters are consistent with a well-defined superhelical model.
- Nicked circular DNA exhibits different liquid crystalline behavior, highlighting the role of supercoiling.