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2100 Biophysical Journal Volume 85 October 2003 21002110 Onset of DNA Aggregation in Presence of Monovalent and
 

Summary: 2100 Biophysical Journal Volume 85 October 2003 21002110
Onset of DNA Aggregation in Presence of Monovalent and
Multivalent Counterions
Yoram Burak, Gil Ariel, and David Andelman
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
ABSTRACT We address theoretically aggregation of DNA segments by multivalent polyamines such as spermine and
spermidine. In experiments, the aggregation occurs above a certain threshold concentration of multivalent ions. We
demonstrate that the dependence of this threshold on the concentration of DNA has a simple form. When the DNA
concentration cDNA is smaller than the monovalent salt concentration, the threshold multivalent ion concentration depends
linearly on cDNA, having the form acDNA 1 b. The coefficients a and b are related to the density profile of multivalent counterions
around isolated DNA chains, at the onset of their aggregation. This analysis agrees extremely well with recent detailed
measurements on DNA aggregation in the presence of spermine. From the fit to the experimental data, the number of
condensed multivalent counterions per DNA chain can be deduced. A few other conclusions can then be reached: 1), the
number of condensed spermine ions at the onset of aggregation decreases with the addition of monovalent salt; 2), the
Poisson-Boltzmann theory overestimates the number of condensed multivalent ions at high monovalent salt concentrations;
and 3), our analysis of the data indicates that the DNA charge is not overcompensated by spermine at the onset of aggregation.
INTRODUCTION
Condensation and aggregation of DNA, induced by mul-
tivalent counterions, have been extensively studied in the
past two decades (for a review, see Bloomfield et al., 2000,

  

Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University

 

Collections: Materials Science; Physics