a Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn , Bonn , Germany.
RNA Biol. 2017 Sep 2;14(9):1197-1208. doi: 10.1080/15476286.2017.1294309. Epub 2017 Feb 17.
Base 37 in tRNA, 3'-adjacent to the anticodon, is occupied by a purine base that is thought to stabilize codon recognition by stacking interactions on the first Watson-Crick base pair. If the first codon position forms an A.U or U.A base pair, the purine is likely further modified in all domains of life. One of the first base modifications found in tRNA is N-isopentenyl adenosine (iA) present in a fraction of tRNAs in bacteria and eukaryotes, which can be further modified to 2-methyl-thio-N-isopentenyladenosine (msiA) in a subset of tRNAs. Homologous tRNA isopentenyl transferase enzymes have been identified in bacteria (MiaA), yeast (Mod5, Tit1), roundworm (GRO-1), and mammals (TRIT1). In eukaryotes, isopentenylation of cytoplasmic and mitochondrial tRNAs is mediated by products of the same gene. Accordingly, a patient with homozygous mutations in TRIT1 has mitochondrial disease. The role of iA in a subset of tRNAs in gene expression has been linked with translational fidelity, speed of translation, skewed gene expression, and non-sense suppression. This review will not cover the action of iA as a cytokinin in plants or the potential function of Mod5 as a prion in yeast.
反密码子 3' 端的 tRNA 碱基 37 被嘌呤碱基占据，该碱基通过与第一个 Watson-Crick 碱基对的堆积相互作用稳定密码子识别。如果第一个密码子位置形成 A.U 或 U.A 碱基对，则嘌呤碱基在所有生命领域都可能进一步修饰。在 tRNA 中发现的第一个碱基修饰之一是 N-异戊烯腺苷（iA），存在于细菌和真核生物的一部分 tRNA 中，它可以在 tRNA 的亚组中进一步修饰为 2-甲基硫代-N-异戊烯腺苷（msiA）。细菌（MiaA）、酵母（Mod5、Tit1）、蛔虫（GRO-1）和哺乳动物（TRIT1）中已鉴定出同源的 tRNA 异戊烯基转移酶。在真核生物中，细胞质和线粒体 tRNA 的异戊烯化由同一基因的产物介导。因此，TRIT1 基因纯合突变的患者会患有线粒体疾病。iA 在部分 tRNA 中在基因表达中的作用与翻译保真度、翻译速度、基因表达偏倚和无意义抑制有关。本综述将不涵盖 iA 在植物中作为细胞分裂素的作用，也不涵盖 Mod5 在酵母中作为朊病毒的潜在功能。
