Onset of DNA aggregation in presence of monovalent and multivalent counterions

Yoram Burak, Gil Ariel, David Andelman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


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 α CDNA + β. The coefficients α and β 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.

Original languageAmerican English
Pages (from-to)2100-2110
Number of pages11
JournalBiophysical Journal
Issue number4
StatePublished - 1 Oct 2003
Externally publishedYes

Bibliographical note

Funding Information:
Support from the Israel Science Foundation under grant No. 210/02, to B.S.F., is gratefully acknowledged. D.A. thanks the Alexander von Humboldt Foundation for a research award.


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