Competitive Effects of 2+ and 3+ Cations on DNA Compaction

C. Tongu; T. Kenmotsu; Y. Yoshikawa; A. A. Zinchenko; N. Chen; K. Yoshikawa

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arXiv · 1601.01392

Competitive Effects of 2+ and 3+ Cations on DNA Compaction

C. Tongu·T. Kenmotsu·Y. Yoshikawa·A. A. Zinchenko·N. Chen·K. Yoshikawa

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Abstract

By using single-DNA observation with fluorescence microscopy, we observed the effects of divalent and trivalent cations on the higher-order structure of giant DNA (T4 DNA with 166 kbp). It was found that divalent cations, such as Mg(2+) and Ca(2+), inhibit DNA compaction induced by a trivalent cation, spermidine (SPD(3+)). On the other hand, in the absence of SPD(3+), divalent cations cause the shrinkage of DNA. These experimental observations are inconsistent with the well-established Debye-Huckel scheme regarding the shielding effect of counter ions, which is given as the additivity of contributions of cations with different valences. We interpreted the competition between 2+ and 3+ cations in terms of the change in the translational entropy of the counter ions before and after the folding transition of DNA. For the compaction with SPD(3+), we considered the increase in translational entropy due to the ion-exchange of the intrinsic monovalent cations condensing on a highly-charged polyelectrolyte, double-stranded DNA, by the 3+ cations. In contrast, the presence of 2+ cation decreases the gain of entropy owe to the ion-exchange between monovalent and 3+ ions.

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C. Tongu, T. Kenmotsu, Y. Yoshikawa, A. A. Zinchenko, N. Chen, K. Yoshikawa. 2016-01-07. Competitive Effects of 2+ and 3+ Cations on DNA Compaction. https://arxiv.org/abs/1601.01392

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