Bhaumik S R, Chary K V, Govil G, Liu K, Miles H T
Chemical Physics Group, Tata Institute of Fundamental Research, Bombay, India.
Nucleic Acids Res. 1995 Oct 25;23(20):4116-21. doi: 10.1093/nar/23.20.4116.
Homo-purine (d-TGAGGAAAGAAGGT) and homo-pyrimidine (d-CTCCTTTCTTCC) oligomers have been designed such that they are complementary in parallel orientation. When mixed in a 1:1 molar ratio, the system adopts an antiparallel duplex at neutral pH with three mismatched base pairs. On lowering the pH below 5.5, a new complex is formed. The NMR results show the coexistence of a intermolecular pyrimidine.purine:pyrimidine DNA triplex and a single stranded oligopurine at this pH. The triplex is stabilized by five T.A:T, four C+.G:C and two mismatched triads, namely, C+.G-T and T.A-C. This triplex is further stabilized by a Hoogsteen C+.G base-pair on one end. Temperature dependence of the imino proton resonances reveals that the triplex dissociates directly into single strands around 55 degrees C, without duplex intermediates. Parallel duplexes are not formed under any of the conditions employed in this study.
同型嘌呤（d-TGAGGAAAGAAGGT）和同型嘧啶（d-CTCCTTTCTTCC）寡聚物被设计成在平行方向上互补。当以1:1摩尔比混合时，该体系在中性pH下形成具有三个错配碱基对的反平行双链体。当pH降至5.5以下时，会形成一种新的复合物。核磁共振结果表明，在此pH下，分子间嘧啶·嘌呤:嘧啶DNA三链体和单链寡嘌呤共存。该三链体由五个T.A:T、四个C⁺.G:C和两个错配三联体（即C⁺.G-T和T.A-C）稳定。该三链体在一端还由一个Hoogsteen C⁺.G碱基对进一步稳定。亚氨基质子共振的温度依赖性表明，该三链体在55摄氏度左右直接解离为单链，没有双链中间体。在本研究采用的任何条件下都不会形成平行双链体。
