THE ROLE OF METAL-IONS IN THE CONFORMATION OF THE 4-WAY DNA JUNCTION
THE ROLE OF METAL-IONS IN THE CONFORMATION OF THE 4-WAY DNA JUNCTION
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DOI：
10.1002/j.1460-2075.1990.tb08146.x
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发表时间：
1990-02-01
期刊：
影响因子：
11.4
通讯作者：
LILLEY, DMJ
中科院分区：
文献类型：
--
作者：
DUCKETT, DR;MURCHIE, AIH;LILLEY, DMJ
金属离子将DNA连接折叠成紧凑的构象，从而保护所有胸腺嘧啶碱基免受四氧化锇的修饰。在没有阳离子的情况下，结的臂以近似正方形平面的构型完全延伸。IIa族阳离子在80-100 μ M下有效地实现了连接的折叠构象，并且在如从凝胶电泳实验中推导出的折叠连接的离子浓度和阻止连接处的四氧化锇反应的离子浓度之间存在极好的一致性。六氨合钴（III）在2 μ M时实现完全折叠，而精胺和亚精胺在25 μ M时有效。一些过渡金属离子如Ni（II）可以取代IIA族阳离子。IA族的单价离子在折叠结中仅部分有效。非常高的浓度是必要的，凝胶电泳迁移率表明，采用不太对称的构象和胸腺嘧啶基地在交界处保持反应性的四氧化锇。在结的中心的电荷-电荷相互作用在结构上极其重要。不带电荷的甲基膦酸酯取代结磷酸基团严重扰乱结的结构。如果只有两个磷酸被取代，直接面对交叉点，结构总是折叠，以便将电中性磷酸置于交换链上。我们认为，折叠成堆叠的X-结构的结产生电负性裂缝，可以选择性地结合金属离子，这取决于化学，大小和离子的电荷。此外，这些空腔的占用是必不可少的结折叠，以减少静电排斥。这些结果表明，金属离子是霍利迪结的组成部分。
Metal ions fold DNA junctions into a compact conformation that confers protection of all thymine bases to modification by osmium tetroxide. In the absence of the cation the arms of the junction are fully extended in an approximately square-planar configuration. Group IIa cations are effective in achieving a folded conformation of the junction at 80-100 .mu.M, and there is an excellent agreement between the ionic concentrations that fold the junctions as deduced from gel electrophoretic experiments, and those that prevent osmium tetroxide reaction at the junction. Hexamminecobalt (III) achieves full folding at 2 .mu.M, while spermine and spermidine are effective at 25 .mu.M. Some transition metal ions such as Ni(II) may replace the group IIA cations. Monovalent ions of group IA are only partially effective in folding the junctions. Very much higher concentrations are necessary, gel electrophoretic mobilities suggest that a less symmetrical conformation is adopted and thymine bases at the junction remain reactive to osmium tetroxide. Charge-charge interactions at the centre of the junction are structurally extremely important. Substitution of junction phosphate groups by uncharged methyl phosphonates severely perturbs the structure of the junction. If just two phosphates are substituted, diametrically facing across the junction, the structure always folds in order to place the electrically neutral phosphate on the exchanging strands. We suggest that folding of the junction into the stacked X-structure generates electronegative clefts that can selectively bind metal ions, depending on the chemistry, size and charge of the ion. Moreover, occupation of these cavities is essential for junction folding, in order to reduce electrostatic repulsion. These results demonstrate that metal ions are an integral component of the Holliday junction.