Dielectric control of counterion-induced single-chain folding transition of DNA
Dielectric control of counterion-induced single-chain folding transition of DNA
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DOI：
10.1529/biophysj.105.059493
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发表时间：
2005-05-01
影响因子：
3.4
通讯作者：
Yoshikawa, K
中科院分区：
文献类型：
--
作者：
Baigl, D;Yoshikawa, K
在冷凝剂的作用下，巨大的双链DNA单链经历了一阶相变，在长螺旋态和折叠致密态之间转换。为了将这种类电荷吸引现象与反离子凝聚联系起来，我们在DNA水溶液中进行了一系列单链实验，通过改变相对介电常数epsilon(r)从80到170来改变反离子凝聚的程度。以四价精胺（SPM4+）为凝聚剂，通过透射电镜和荧光显微镜观察了巨DNA单链构象的变化。在固定的介电常数下，单DNA链在加入精胺后折叠成紧致状态，而在恒定的精胺浓度下，单DNA链随着ε (r)的增加而展开。在这两种情况下，过渡在单链水平上基本上是离散的。我们发现，随着介电常数的增加，诱导单链折叠转变所需的精胺临界浓度呈指数增长，对应于87 - 88%的DNA电荷在转变开始时被中和。我们还观察到，当epsilon(r)增加时，紧凑DNA的环状形态部分展开。
In the presence of condensing agents, single chains of giant double-stranded DNA undergo a first-order phase transition between an elongated coil state and a folded compact state. To connect this like-charged attraction phenomenon to counterion condensation, we performed a series of single-chain experiments on aqueous solutions of DNA, where we varied the extent of counterion condensation by varying the relative dielectric constant epsilon(r) from 80 to 170. Single-chain observations of changes in the conformation of giant DNA were performed by transmission electron microscopy and fluorescence microscopy, with tetravalent spermine (SPM4+) as a condensing agent. At a fixed dielectric constant, single DNA chains fold into a compact state upon the addition of spermine, whereas at a constant spermine concentration single DNA chains unfold with an increase in epsilon(r). In both cases, the transition is largely discrete at the level of single chains. We found that the critical concentration of spermine necessary to induce the single-chain folding transition increases exponentially as the dielectric constant increases, corresponding to 87 - 88% of the DNA charge neutralized at the onset of the transition. We also observed that the toroidal morphology of compact DNA partially unfolds when epsilon(r) is increased.