title: Divalent cation shrinks DNA but inhibits its compaction with trivalent cation.
abstract: Our observation reveals the effects of divalent and trivalent cations on the higher-order structure of giant DNA (T4 DNA 166 kbp) by fluorescence microscopy. It was found that divalent cations, 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. As the control experiment, we have confirmed the minimum effect of monovalent cation, Na(+) on the DNA higher-order structure. We interpret the competition between 2+ and 3+ cations in terms of the change in the translational entropy of the counterions. For the compaction with SPD(3+), we consider 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 contribution by the ion-exchange between monovalent and 3+ ions.
authors.affiliation: Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe 610-0321, Japan.
authors.forename: Chika
authors.initials: C
authors.lastname: Tongu
authors.affiliation: Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe 610-0321, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kenmotsu
authors.affiliation: Research Organization of Science and Technology, Ritsumeikan University, Kusatsu 525-8577, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yoshikawa
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Anatoly
authors.initials: A
authors.lastname: Zinchenko
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Ning
authors.initials: N
authors.lastname: Chen
authors.affiliation: Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe 610-0321, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Yoshikawa
mesh_terms: D002413:Cations, Divalent / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D019277:Entropy; D008856:Microscopy, Fluorescence; D012964:Sodium / Q000737:chemistry
chemical_list: D002413:Cations, Divalent; D004247:DNA; D012964:Sodium