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Dimensions of plectonemically supercoiled DNA.
Svetlana S Zakharova1, Wim Jesse, Claude Backendorf
1Leiden Institute of Chemistry, Leiden University, 2300 RA Leiden, The Netherlands.
Biophysical Journal
|July 19, 2002
Summary
Small angle neutron scattering reveals that plectonemically supercoiled DNA adopts an interwound configuration. DNA compaction decreases supercoil radius and pitch, increasing duplex twist, which may drive liquid-crystalline phase transitions.
Area of Science:
- Biophysics
- Structural Biology
- Polymer Physics
Background:
- Supercoiled DNA plays crucial roles in cellular processes.
- Understanding DNA's higher-order structure is essential for molecular biology.
Purpose of the Study:
- To determine the configuration and regularity of plectonemically supercoiled DNA.
- To investigate the structural changes of supercoiled DNA under varying concentrations.
Main Methods:
- Small angle neutron scattering (SANS) measurements on pUC18 plasmid DNA in saline solutions.
- Derivation of a mathematical model for the scattering function of superhelical structures.
- Analysis of structural parameters including opening angle, radius, and pitch.
Main Results:
- An interwound configuration accurately describes the supercoiled DNA structure.
- A constant opening angle of approximately 58 degrees was observed, with distributions in radius and pitch.
- DNA compaction at higher concentrations led to decreased radius and pitch, accompanied by increased duplex twist.
Conclusions:
- The interwound model, accounting for inter-supercoil interactions, explains the observed scattering data.
- Structural results align with independent measurements of linking number deficit in dilute solutions.
- The observed compaction-induced twist is hypothesized to be critical for the transition to the liquid-crystalline phase of DNA.