van den Hoogen Y T, van Beuzekom A A, van den Elst H, van der Marel G A, van Boom J H, Altona C
Gorlaeus Laboratories, Leiden University, The Netherlands.
Nucleic Acids Res. 1988 Apr 11;16(7):2971-86. doi: 10.1093/nar/16.7.2971.
NMR and model-building studies were carried out on the duplex d(CTGGTGCGG).d(CCGCCCAG), referred to as (9+8)-mer, which contains an unpaired thymidine residue. Resonances of the base and of several sugar protons of the (9+8)-mer were assigned by means of a NOESY experiment. Interresidue NOEs between dG(4) and dT(5) as well as between dT(5) and dG(6) provided evidence that the extra dT is stacked into the duplex. Thermodynamic analysis of the chemical shift vs temperature profiles yielded an average TmD value of 334 K and delta HD of -289 kJmol-1 for the duplex in equilibrium random-coil transition. The shapes of the shift profiles as well as the thermodynamic parameters obtained for the extra dT residue and its neighbours again indicate that the unpaired dT base is incorporated inside an otherwise intact duplex. This conclusion is further supported by (a) the observation of an imino-proton resonance of the unpaired dT; (b) the relatively small dispersion in 31P chemical shifts (approximately 0.5 ppm) for the (9+8)-mer, which indicates the absence of t/g or g/t combinations for the phosphate diester torsion angles alpha/zeta. An energy-minimized model of the (9+8)-mer, which fits the present collection of experimental data, is presented.
对双链体d(CTGGTGCGG).d(CCGCCCAG)(称为(9 + 8) - 聚体)进行了核磁共振(NMR)和模型构建研究,该双链体含有一个未配对的胸腺嘧啶残基。通过核Overhauser效应光谱(NOESY)实验确定了(9 + 8) - 聚体中碱基和几个糖质子的共振峰。dG(4)与dT(5)以及dT(5)与dG(6)之间的残基间核Overhauser效应(NOE)提供了额外的dT堆积在双链体中的证据。化学位移随温度变化曲线的热力学分析得出,在平衡随机卷曲转变中,双链体的平均解链温度(TmD)值为334 K,焓变(ΔHD)为 - 289 kJ/mol。额外dT残基及其相邻残基的位移曲线形状以及获得的热力学参数再次表明,未配对的dT碱基掺入了原本完整的双链体内部。这一结论得到了以下几点的进一步支持:(a) 观察到未配对dT的亚氨基质子共振;(b) (9 + 8) - 聚体的31P化学位移相对较小(约0.5 ppm),这表明磷酸二酯扭转角α/ζ不存在t/g或g/t组合。本文给出了一个能量最小化的(9 + 8) - 聚体模型,该模型符合目前收集的实验数据。