Figueroa N, Keith G, Leroy J L, Plateau P, Roy S, Gueron M
Proc Natl Acad Sci U S A. 1983 Jul;80(14):4330-3. doi: 10.1073/pnas.80.14.4330.
We have monitored the exchange of imino and amino protons by NMR after quick transfer of yeast tRNAAsp in 2H2O solvent. When the concentration of exchange-catalyzing buffer is not too high, one imino proton exchanges considerably more slowly than any other (e.g., 100 hr versus 4 hr for the second-slowest imino proton at 18 degrees C in 15 mM Mg). This provides excellent conditions for identification, by the nuclear Overhauser effect, of the slowest exchanging proton, which we show to be the imino proton of the U-8 . A-14 reverse Hoogsteen tertiary-structure base pair; other slowly exchanging protons are identified as imino protons from A . U-11 and G . psi-13. In preliminary experiments, we find that the exchange of these protons is catalyzed by cacodylate or Tris buffer. The lifetimes of two other imino protons, ca. 10 min at 28 degrees C, are buffer independent. Slowly exchanging amino protons have also been observed. Correlation with the exchange of the uracil-8 imino proton suggests that they may be from adenine-14.
在将酵母天冬氨酸转运核糖核酸快速转移至重水（2H₂O）溶剂后，我们通过核磁共振监测了亚氨基和氨基质子的交换情况。当交换催化缓冲液的浓度不太高时，有一个亚氨基质子的交换速度明显慢于其他任何一个（例如，在15 mM镁离子存在下，18摄氏度时，最慢的亚氨基质子交换时间为100小时，而第二慢的为4小时）。这为通过核Overhauser效应鉴定最慢交换质子提供了绝佳条件，我们发现最慢交换的质子是U-8的亚氨基质子，它参与A-14反向Hoogsteen三级结构碱基对的形成；其他交换较慢的质子被鉴定为来自A·U-11和G·ψ-13的亚氨基质子。在初步实验中，我们发现这些质子的交换由二甲胂酸盐或Tris缓冲液催化。另外两个亚氨基质子在28摄氏度时的寿命约为10分钟，且与缓冲液无关。我们还观察到了交换较慢的氨基质子。与尿嘧啶-8亚氨基质子交换的相关性表明，它们可能来自腺嘌呤-14。
