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Related Experiment Videos

DNA persistence length revisited.

Y Lu1, B Weers, N C Stellwagen

  • 1Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.

Biopolymers
|July 13, 2002
PubMed
Summary

Transient electric birefringence measurements reveal DNA flexibility. DNA persistence length decreases with increasing salt concentration and shows a slight temperature dependence, while hydrodynamic radius remains constant.

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Physical Chemistry

Background:

  • Understanding DNA flexibility is crucial for molecular biology and biophysics.
  • Previous studies have explored DNA's physical properties, but data at low ionic strengths and varying temperatures require further elucidation.

Purpose of the Study:

  • To characterize DNA restriction fragments using transient electric birefringence (TEB).
  • To determine the persistence length (p) and hydrodynamic radius (r) of DNA as a function of temperature and ionic strength.
  • To identify the most suitable hydrodynamic model for describing DNA flexibility in low ionic strength solutions.

Main Methods:

  • Transient electric birefringence (TEB) measurements were performed on DNA fragments (79-789 bp) at temperatures ranging from 4 to 43°C.
  • Rotational relaxation times were obtained by fitting TEB field-free decay signals.
  • Persistence length (p) and hydrodynamic radius (r) were calculated using various hydrodynamic models, with a focus on the wormlike chain model combined with the revised Broersma equation.

Main Results:

  • The wormlike chain model with the revised Broersma equation best described DNA flexibility in low ionic strength solutions.
  • Consensus hydrodynamic radius (r) was 14.7 ± 0.4 Å at 20°C, independent of temperature.
  • Consensus persistence length (p) decreased from ~564 Å (0.2-1 mM NaCl) to 440 Å (0.2 mM Mg2+), exhibiting a shallow maximum at 20°C.

Conclusions:

  • The study provides model-dependent values for DNA persistence length and hydrodynamic radius.
  • DNA flexibility is influenced by ionic strength, with Mg2+ ions causing a greater reduction in persistence length than Na+ ions.
  • The determined physical parameters of DNA contribute to a better understanding of its behavior in solution.

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