Gamble R C, Schimmel P R
Proc Natl Acad Sci U S A. 1974 Apr;71(4):1356-60. doi: 10.1073/pnas.71.4.1356.
The incorporation of tritium into the C-8 position of purine residues in yeast tRNA(Phe) is shown to be markedly dependent on the conformation of the molecule. The completely unfolded molecule incorporates tritium at a rate commensurate to that expected for free purine nucleotides, but partially or completely folded forms incorporate proportionately less. The labeling of specific purine sites is determined by digesting the nucleic acid with a specific nuclease and analyzing each of the radioactive fragments produced. This analysis reveals that the amount of labeling of a purine in the folded form is strongly dependent upon its position in the sequence, whereas purine labeling in the unfolded form is independent of sequence position. The labeling pattern of the different bases in the folded form agrees fairly well with what is expected, based on existing solution and x-ray data on the conformation, i.e., residues involved in helical sections or apparently masked by tertiary interactions label more slowly than those on the "outside" of the molecule. Finally, folding and unfolding of specific regions of the macromolecule may be followed by the isotope labeling.
氚掺入酵母苯丙氨酸转运核糖核酸（tRNA(Phe)）嘌呤残基的C-8位置，结果表明这明显取决于分子的构象。完全展开的分子以与游离嘌呤核苷酸预期速率相当的速度掺入氚，但部分或完全折叠的形式掺入比例相对较少。通过用特定核酸酶消化核酸并分析产生的每个放射性片段来确定特定嘌呤位点的标记。该分析表明，折叠形式中嘌呤的标记量强烈取决于其在序列中的位置，而未折叠形式中的嘌呤标记与序列位置无关。基于现有的关于构象的溶液和X射线数据，折叠形式中不同碱基的标记模式与预期相当吻合，即参与螺旋部分或明显被三级相互作用掩盖的残基比分子“外部”的残基标记得更慢。最后，大分子特定区域的折叠和展开可以通过同位素标记来追踪。
