Expression génétique microbienne, Université Paris Cité, CNRS, Institut de biologie physico-chimique, Paris, France.
Department of Chemistry, Ludwig Maximilians University, Munich, Germany.
Nucleic Acids Res. 2023 Oct 27;51(19):10653-10667. doi: 10.1093/nar/gkad722.
As essential components of the protein synthesis machinery, tRNAs undergo a tightly controlled biogenesis process, which include the incorporation of numerous posttranscriptional modifications. Defects in these tRNA maturation steps may lead to the degradation of hypomodified tRNAs by the rapid tRNA decay (RTD) and nuclear surveillance pathways. We previously identified m1A58 as a late modification introduced after modifications Ψ55 and T54 in yeast elongator tRNAPhe. However, previous reports suggested that m1A58 is introduced early during the tRNA modification process, in particular on primary transcripts of initiator tRNAiMet, which prevents its degradation by RNA decay pathways. Here, aiming to reconcile this apparent inconsistency on the temporality of m1A58 incorporation, we examined its introduction into yeast elongator and initiator tRNAs. We used specifically modified tRNAs to report on the molecular aspects controlling the Ψ55 → T54 → m1A58 modification circuit in elongator tRNAs. We also show that m1A58 is efficiently introduced on unmodified tRNAiMet, and does not depend on prior modifications. Finally, we show that m1A58 has major effects on the structural properties of initiator tRNAiMet, so that the tRNA elbow structure is only properly assembled when this modification is present. This observation provides a structural explanation for the degradation of hypomodified tRNAiMet lacking m1A58 by the nuclear surveillance and RTD pathways.
作为蛋白质合成机器的重要组成部分，tRNA 经历了严格控制的生物发生过程，其中包括许多转录后修饰的掺入。这些 tRNA 成熟步骤的缺陷可能导致修饰不足的 tRNA 通过快速 tRNA 降解（RTD）和核监测途径降解。我们之前发现 m1A58 是在酵母延伸 tRNAPhe 的 Ψ55 和 T54 修饰之后引入的晚期修饰。然而，之前的报告表明，m1A58 是在 tRNA 修饰过程的早期引入的，特别是在起始 tRNAiMet 的初级转录物上，这可以防止其被 RNA 降解途径降解。在这里，为了调和 m1A58 掺入的时间上的这种明显不一致性，我们检查了其在酵母延伸和起始 tRNA 中的引入。我们使用经过专门修饰的 tRNA 来报告控制延伸 tRNA 中 Ψ55→T54→m1A58 修饰回路的分子方面。我们还表明，m1A58 可以有效地引入未经修饰的 tRNAiMet 中，并且不依赖于先前的修饰。最后，我们表明 m1A58 对起始 tRNAiMet 的结构特性有重大影响，因此只有在存在该修饰时，tRNA 肘结构才能正确组装。这一观察结果为缺乏 m1A58 的修饰不足的 tRNAiMet 通过核监测和 RTD 途径降解提供了结构解释。
