Sturchler C, Westhof E, Carbon P, Krol A
Unité CNRS Structure des Macromolécules Biologiques et Mécanismes de Reconnaissance, Institut de Biologie Moléculaire et Cellulaire, Strasbourg, France.
Nucleic Acids Res. 1993 Mar 11;21(5):1073-9. doi: 10.1093/nar/21.5.1073.
Cotranslational insertion of selenocysteine into selenoenzymes is mediated by a specialized transfer RNA, the tRNA(Sec). We have carried out the determination of the solution structure of the eucaryotic tRNA(Sec). Based on the enzymatic and chemical probing approach, we show that the secondary structure bears a few unprecedented features like a 9 bp aminoacid-, a 4 bp thymine- and a 6 bp dihydrouridine-stems. Surprisingly, the eighth nucleotide, although being a uridine, is base-paired and cannot therefore correspond to the single-stranded invariant U8 found in all tRNAs. Rather, experimental evidence led us to propose that the role of the invariant U8 is actually played by the tenth nucleotide which is an A, numbered A8 to indicate this fact. The experimental data therefore demonstrate that the cloverleaf structure we derived experimentally resembles the hand-folded model proposed by Böck et al (ref. 3). Using the solution data and computer modelling, we derived a three-dimensional structure model which shows some unique aspects. Basically, A8, A14, U21 form a novel type of tertiary interaction in which A8 interacts with the Hoogsteen sites of A14 which itself forms a Watson-Crick pair with U21. No coherent model containing the canonical 15-48 interaction could be derived. Thus, the number of tertiary interactions appear to be limited, leading to an uncoupling of the variable stem from the rest of the molecule.
硒代半胱氨酸共翻译插入硒酶是由一种特殊的转运RNA（tRNA(Sec)）介导的。我们已经对真核生物tRNA(Sec)的溶液结构进行了测定。基于酶促和化学探测方法，我们发现其二级结构具有一些前所未有的特征，如一个9碱基对的氨基酸茎、一个4碱基对的胸腺嘧啶茎和一个6碱基对的二氢尿嘧啶茎。令人惊讶的是，第八个核苷酸虽然是尿苷，但却形成了碱基对，因此不可能对应于所有tRNA中发现的单链不变U8。相反，实验证据使我们提出，不变U8的作用实际上由第十个核苷酸发挥，它是一个A，编号为A8以表明这一事实。因此，实验数据表明，我们通过实验得出的三叶草结构类似于Böck等人提出的手折叠模型（参考文献3）。利用溶液数据和计算机建模，我们推导出了一个三维结构模型，该模型显示出一些独特的方面。基本上，A8、A14、U21形成了一种新型的三级相互作用，其中A8与A14的Hoogsteen位点相互作用，而A14本身与U21形成沃森-克里克配对。无法得出包含典型15-48相互作用的连贯模型。因此，三级相互作用的数量似乎有限，导致可变茎与分子的其余部分解耦。
