Vlassakis Julea, Williams Jeremy, Hatch Kristi, Danilowicz Claudia, Coljee Vincent W, Prentiss Mara
Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts 02138, USA.
J Am Chem Soc. 2008 Apr 16;130(15):5004-5. doi: 10.1021/ja0776576. Epub 2008 Mar 22.
We examine the interaction between monovalent cations and DNA using several different assays that measure the stability of double-stranded DNA (dsDNA). The thermal melting of dsDNA and the mechanical separation of dsDNA into two single strands both depend on the stability of dsDNA with respect to ssDNA and are sensitive to the interstrand phosphate repulsion. We find that the experimentally measured melting temperatures and unzipping forces are approximately the same for all of the ions considered in this study. Likewise, the force required to transform B-DNA into the overstretched form is also similar for all of the ions. In contrast, for a given ion concentration, the force at which the overstretched state fully relaxes back to the canonical B-DNA form depends on the cation; however, for all cations, the overstretching force decreases with decreasing ion concentration, suggesting that this force is sensitive to screening. We observe a general trend for smaller ions to produce more efficient relaxation. Finally, for a given cation, the relaxation can also depend on the anion.
我们使用几种不同的测定方法来研究单价阳离子与DNA之间的相互作用，这些方法用于测量双链DNA（dsDNA）的稳定性。dsDNA的热解链以及将dsDNA机械分离成两条单链都取决于dsDNA相对于单链DNA（ssDNA）的稳定性，并且对链间磷酸排斥敏感。我们发现，对于本研究中考虑的所有离子，实验测量的解链温度和拉开双链的力大致相同。同样，将B-DNA转变为过度拉伸形式所需的力对于所有离子也相似。相比之下，对于给定的离子浓度，过度拉伸状态完全松弛回到标准B-DNA形式时的力取决于阳离子；然而，对于所有阳离子，过度拉伸力随离子浓度降低而减小，这表明该力对屏蔽敏感。我们观察到较小离子产生更有效松弛的一般趋势。最后，对于给定的阳离子，松弛也可能取决于阴离子。
