Wende Sandra, Platzer Edward G, Jühling Frank, Pütz Joern, Florentz Catherine, Stadler Peter F, Mörl Mario
University of Leipzig, Institute for Biochemistry, Leipzig, Germany.
University of California, Riverside, Department of Nematology, Riverside, CA 92521, USA.
Biochimie. 2014 May;100:151-8. doi: 10.1016/j.biochi.2013.07.034. Epub 2013 Aug 17.
Due to their function as adapters in translation, tRNA molecules share a common structural organization in all kingdoms and organelles with ribosomal protein biosynthesis. A typical tRNA has a cloverleaf-like secondary structure, consisting of acceptor stem, D-arm, anticodon arm, a variable region, and T-arm, with an average length of 73 nucleotides. In several mitochondrial genomes, however, tRNA genes encode transcripts that show a considerable deviation of this standard, having reduced D- or T-arms or even completely lack one of these elements, resulting in tRNAs as small as 66 nts. An extreme case of such truncations is found in the mitochondria of Enoplea. Here, several tRNA genes are annotated that lack both the D- and the T-arm, suggesting even shorter transcripts with a length of only 42 nts. However, direct evidence for these exceptional tRNAs, which were predicted by purely computational means, has been lacking so far. Here, we demonstrate that several of these miniaturized armless tRNAs consisting only of acceptor- and anticodon-arms are indeed transcribed and correctly processed by non-encoded CCA addition in the mermithid Romanomermis culicivorax. This is the first direct evidence for the existence and functionality of the smallest tRNAs ever identified so far. It opens new possibilities towards exploration/assessment of minimal structural motifs defining a functional tRNA and their evolution.
由于tRNA分子在翻译过程中充当衔接子，在所有生物界和细胞器中，其与核糖体蛋白生物合成具有共同的结构组织。典型的tRNA具有三叶草状二级结构，由受体茎、D臂、反密码子臂、可变区和T臂组成，平均长度为73个核苷酸。然而，在一些线粒体基因组中，tRNA基因编码的转录本与该标准有相当大的偏差，D臂或T臂缩短，甚至完全缺失其中一个元件，导致tRNA小至66个核苷酸。这种截短的极端情况见于线虫纲动物的线粒体。在这里，有几个tRNA基因被注释为既没有D臂也没有T臂，这表明转录本甚至更短，只有42个核苷酸。然而，到目前为止，缺乏关于这些通过纯计算方法预测的特殊tRNA的直接证据。在这里，我们证明了在食蚊索线虫中，几个仅由受体臂和反密码子臂组成的小型无臂tRNA确实被转录，并通过非编码的CCA添加进行了正确加工。这是迄今为止所鉴定出的最小tRNA存在及其功能的首个直接证据。它为探索/评估定义功能性tRNA的最小结构基序及其进化开辟了新的可能性。
