Fazakerley G V, van der Marel G A, van Boom J H, Guschlbauer W
Nucleic Acids Res. 1984 Nov 12;12(21):8269-79. doi: 10.1093/nar/12.21.8269.
All exchangeable protons in a short DNA helix, d(CG)3 sodium salt, have been studied by proton nuclear magnetic resonance. The cytidine and guanosine amino protons have been assigned for the first time. As a function of temperature the cytidine amino protons and the imino protons behave very similarly, their relaxation is dominated by exchange with solvent above 30 degrees C. The guanosine amino protons, however, show that helix opening can only be described by a multistate model. The most rapid process observed is probably a twist about the helix axis which lengthens or breaks the guanosine amino hydrogen bond and allows rotation of the amino group. The second fastest process is a scissor opening into the major groove which gives rise to solvent exchange with the imino and cytidine amino protons. The slowest process observed is the complete base pair opening in which the guanosine amino protons also exchange with solvent. For the ammonium salt of the oligonucleotide, a specific ammonium ion complex is observed which at low temperature may catalyze exchange of the guanosine amino protons with the protons of the ammonium ion, but retards exchange with solvent. The complex appears to be specific for the sequence d(CpG).
通过质子核磁共振对短DNA螺旋d(CG)3钠盐中的所有可交换质子进行了研究。首次确定了胞嘧啶和鸟嘌呤的氨基质子。作为温度的函数，胞嘧啶氨基质子和亚氨基质子的行为非常相似，在30摄氏度以上，它们的弛豫主要由与溶剂的交换主导。然而，鸟嘌呤氨基质子表明，螺旋的打开只能用多态模型来描述。观察到的最快过程可能是围绕螺旋轴的扭转，这会延长或破坏鸟嘌呤氨基氢键，并允许氨基旋转。第二快的过程是向大沟的剪刀式打开，这导致亚氨基和胞嘧啶氨基质子与溶剂交换。观察到的最慢过程是完全碱基对打开，其中鸟嘌呤氨基质子也与溶剂交换。对于寡核苷酸的铵盐，观察到一种特定的铵离子复合物，在低温下，它可能催化鸟嘌呤氨基质子与铵离子质子的交换，但会阻碍与溶剂的交换。该复合物似乎对序列d(CpG)具有特异性。
