Structural analysis of the (dA)10.2(dT)10 triple helix.
Structural analysis of the (dA)10.2(dT)10 triple helix.
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DOI：
10.1073/pnas.87.5.1942
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发表时间：
1990-03
影响因子：
11.1
通讯作者：
D. S. Pilch;C. Levenson;R. Shafer
中科院分区：
文献类型：
--
作者：
D. S. Pilch;C. Levenson;R. Shafer
体外DNA三螺旋的存在已被发现一段时间。最近的证据表明，DNA三链体存在于体内，并显示其潜在的化疗应用重新关注这些三链构象。然而，目前对这些不寻常的核酸形式的结构信息知之甚少。我们已经诱导和稳定的三重螺旋（dA）10.2（dT）10与氯化镁在中性pH值。UV混合曲线表明1：2（dA）10（dT）10在合适的氯化镁浓度的化学计量。热变性谱建立了一种解链机制，其特征在于第三条链的初始损失，随后是剩余双链体的解离。三链体形式的圆二色性光谱不同于（dA）10中等摩尔的双链体。NMR研究表明，镁诱导的三链体的形成是伴随着一个高场位移的几个亚氨基质子共振之前存在的稳定的三链体形式与氯化镁和诱导新的高场亚氨基质子共振。对未氘化和C8-H-氘化（dA）10.2（dT）10三链体的核Overhauser效应光谱测量表明，可分辨亚氨基蛋白质与腺嘌呤C8-H和C2-H芳香族质子之间存在偶极接触。因此，MgCl 2稳定三链体结构，其中胸腺嘧啶N3-H亚氨基质子参与沃森-克里克和Hoogsteen碱基配对。
The existence of DNA triple helices in vitro has been known for some time. Recent evidence suggesting that DNA triplexes exist in vivo and showing their potential for chemotherapeutic applications has renewed interest in these triple-strand conformations. However, little structural information is currently known about these unusual nucleic acid forms. We have induced and stabilized triple-helical (dA)10.2(dT)10 with MgCl2 at neutral pH. UV mixing curves demonstrate a 1:2 (dA)10 to (dT)10 stoichiometry at suitable MgCl2 concentrations. Thermal denaturation profiles establish a melting mechanism characterized by the initial loss of the third strand, followed by dissociation of the remaining duplex. The circular dichroic spectrum of the triplex form is distinct from that of a duplex equimolar in (dA)10. NMR studies show that magnesium-induced triplex formation is accompanied by an upfield shift of several imino proton resonances present before stabilization of the triplex form with MgCl2 and the induction of new upfield imino proton resonances. Nuclear Overhauser effect spectroscopy measurements on both undeuterated and C8--H-deuterated (dA)10.2(dT)10 triplexes demonstrate dipolar contacts between resolvable imino proteins and both adenine C8--H and C2--H aromatic protons. Hence, MgCl2 stabilizes a triplex structure in which thymine N3--H imino protons are involved in both Watson-Crick and Hoogsteen base pairing.