Romby P, Carbon P, Westhof E, Ehresmann C, Ebel J P, Ehresmann B, Giegé R
Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, France.
J Biomol Struct Dyn. 1987 Dec;5(3):669-87. doi: 10.1080/07391102.1987.10506419.
The conformation of the T-loop of yeast tRNA(Asp) was studied by structural mapping techniques using chemical and enzymatic probes and by three-dimensional graphics modeling with the known crystallographic structures of tRNAs as references. The structural importance of C61 (conserved in the T-stem of all tRNAs) for the loop conformation was directly checked by ethylnitrosourea phosphate alkylation, either on the 3'-half tRNAAsp molecule or on a variant in which C61 was replaced by U61. The reactivity of P60 against ethylnitrosourea alkylation in the variant emphasizes the role of the hydrogen bond between this phosphate and position N4 of C61 for stabilizing the conformation of the T-loop. Experiments on several tRNA variants, containing C61 but altered in the sequence or in the length of the T-loop, indicate that other structural features help to stabilize the hydrogen bond network around P60. Evidence is presented that the reverse Hoogsteen base pair T54-A58 contributes to this stabilization by maintaining the hydrogen bonding between the 2'OH of ribose 58 and P60. Using graphics modeling and based on the chemical data. T-loops of several variants were constructed. It appears that both the constant length of the T-loop and the presence of psi 55 are crucial for the correct interaction between the T- and D-loops. The conclusion of this study is that the T-loop in tRNA possesses an intrinsic conformation (mainly governed by the constant residues) existing primarily without the structural context of the entire tRNA molecule.
通过使用化学和酶促探针的结构测绘技术，并以已知的tRNA晶体结构为参考进行三维图形建模，研究了酵母tRNA（Asp）T环的构象。通过磷酸乙基亚硝基脲烷基化直接检查了C61（在所有tRNA的T茎中保守）对环构象的结构重要性，该烷基化作用于3'-半tRNAAsp分子或C61被U61取代的变体上。变体中P60对磷酸乙基亚硝基脲烷基化的反应性强调了该磷酸与C61的N4位之间的氢键在稳定T环构象中的作用。对几种含有C61但T环序列或长度发生改变的tRNA变体进行的实验表明，其他结构特征有助于稳定P60周围的氢键网络。有证据表明，反向Hoogsteen碱基对T54-A58通过维持核糖58的2'OH与P60之间的氢键来促进这种稳定作用。利用图形建模并基于化学数据，构建了几种变体的T环。看来T环的恒定长度和psi 55 的存在对于T环和D环之间的正确相互作用至关重要。这项研究的结论是，tRNA中的T环具有一种内在构象（主要由恒定残基决定），主要在没有整个tRNA分子的结构背景的情况下存在。
