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首页> 外文期刊>Nucleic Acids Research >Circular dichroism and UV melting studies on formation of an intramolecular triplex containing parallel T*A:T and G*G:C triplets: netropsin complexation with the triplex.
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Circular dichroism and UV melting studies on formation of an intramolecular triplex containing parallel T*A:T and G*G:C triplets: netropsin complexation with the triplex.

机译：循环二色性和UV熔融研究，以形成分子内三元组，其中包含平行的T * A：T和G * G：C三元组：netropsin与三元组的络合。

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摘要

We have used circular dichroism and UV absorption spectroscopy to characterize the formation and melting behaviour of an intramolecular DNA triple helix containing parallel T*A:T and G*G:C triplets. Our approach to induce and to stabilize a parallel triplex involves the oligonucleotide 5'-d(G4A4G4[T4]C4T4C4-[T4]G4T4G4) ([T4] represents a stretch of four thymine residues). In a 10 mM sodium cacodylate, 0.2 mM disodium EDTA (pH 7) buffer, we have shown the following significant results. (i) While in the absence of MgCl2 this oligonucleotide adopts an intramolecular hairpin duplex structure prolonged by the single strand extremity 5'-d([T4]G4T4G4), the presence of millimolar concentrations of MgCl2generates an intramolecular triplex (via double hairpin formation). (ii) In contrast to the antiparallel triplex formed by the oligonucleotide 5'-d(G4T4G4[T4]G4A4G4[T4]C4T4C4), the parallel triplex melts in a biphasic manner (a triplex to duplex transition followed by a duplex to coil transition) and is less stable than the antiparallel one. The enthalpy change associated with triplex formation (-37 kcal/mol) is approximately half that of duplex formation (-81 kcal/mol). (iii) The parallel triple helix is disrupted by increasing the concentration of KCl(>10 mM), whereas, under the same conditions, the antiparallel triplex remains stable. (iv) Netropsin, a natural DNA minor groove-binding ligand, binds to the central site A4/T4of the duplex or triplex in an equimolar stoichiometry. Its association constant K is smaller for the parallel triplex ( approximately 1 x 10(7) M-1) than for the antiparallel one ( approximately 1 x 10(8) M-1). In contrast to the antiparallel structure, netropsin binding has no apparent effect on thermal stability of the parallel triple helix.
机译：我们已经使用圆二色性和紫外吸收光谱来表征分子内DNA三重螺旋的形成和熔化行为，该三螺旋包含平行的T * A：T和G * G：C三胞胎。我们诱导和稳定平行三链体的方法涉及寡核苷酸5'-d（G4A4G4 [T4] C4T4C4- [T4] G4T4G4）（[T4]代表四个胸腺嘧啶残基的延伸）。在10 mM co酸钠，0.2 mM EDTA二钠（pH 7）缓冲液中，我们显示了以下重要结果。 （i）尽管在缺少MgCl2的情况下，该寡核苷酸采用了分子内发夹双链体结构，并延长了单链末端5'-d（[T4] G4T4G4），但浓度为毫摩尔的MgCl2会生成分子内三联体（通过双发夹形成） 。 （ii）与寡核苷酸5'-d（G4T4G4 [T4] G4A4G4 [T4] C4T4C4）形成的反平行三链体相反，平行三链体以双相方式融化（三链体向双链体过渡，然后由双链体向线圈过渡） ），并且稳定性不如反平行。与三链体形成相关的焓变（-37 kcal / mol）约为双链体形成焓变化的一半（-81 kcal / mol）。 （iii）增加KCl（> 10 mM）的浓度会破坏平行的三重螺旋，而在相同条件下，反平行的三重螺旋保持稳定。 （iv）Netropsin是一种天然的DNA小沟结合配体，以等摩尔化学计量法结合到双链体或三链体的中心位点A4 / T4。对于平行三元组（大约1 x 10（7）M-1），其关联常数K小于反平行三元组的关联常数K（大约1 x 10（8）M-1）。与反平行结构相反，netropsin结合对平行三重螺旋的热稳定性没有明显影响。

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