Bubienko E, Uniack M A, Borer P N
Biochemistry. 1981 Nov 24;20(24):6987-94. doi: 10.1021/bi00527a032.
Comparative studies of the thermally induced helix--coil transition in ribosyl (A-G-C-U)2 and (A-C-G-U)2 are described. Ordered structures form at low temperatures where the ribofuranose rings adopt the 3'-endo conformation and both oligomer helices have base-paired stacking arrangements qualitatively similar to the A-RNA family configuration. Especially for (A-C-G-U)2, there is a lack of quantitative agreement between the A-family base overlap and the 1H NMR data; ring-current and atomic diamagnetic anisotropies using A-form structures fail to predict five of the seven aromatic C--H resonances within 0.2 ppm. The NMR results are in better agreement with the A form for (A-G-C-U)2. For both oligomers, the changes in chemical shift for the anomeric (H1') resonances indicate substantial (greater than or equal to 20 degrees) changes in the average glycosidic torsion angle upon base pairing and stacking for the adenosine and cytidine residues; this angle in uridine and guanosine residues must change only slightly.
描述了核糖基（A - G - C - U）₂和（A - C - G - U）₂中热诱导的螺旋 - 线圈转变的比较研究。在低温下形成有序结构，此时呋喃核糖环采取3'-内型构象，并且两个低聚物螺旋都具有与A - RNA家族构型定性相似的碱基配对堆积排列。特别是对于（A - C - G - U）₂，A家族碱基重叠与¹H NMR数据之间缺乏定量一致性；使用A形式结构的环电流和原子抗磁各向异性未能在0.2 ppm范围内预测七个芳香族C - H共振中的五个。对于（A - G - C - U）₂，NMR结果与A形式更一致。对于这两种低聚物，端基（H1'）共振的化学位移变化表明，腺苷和胞苷残基在碱基配对和堆积时平均糖苷扭转角发生了显著（大于或等于20度）变化；尿苷和鸟苷残基中的这个角度变化一定很小。
