Maréchal-Drouard L, Kumar R, Remacle C, Small I
Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, Strasbourg, France.
Nucleic Acids Res. 1996 Aug 15;24(16):3229-34. doi: 10.1093/nar/24.16.3229.
Larch mitochondria contain a'native'tRNAHis which is absent from angiosperms. Sequence comparisons of genomic DNA and cDNA obtained from unprocessed primary transcripts of the larch mitochondrial gene trnH encoding this tRNA revealed three nucleotide discrepancies. These three nucleotide alterations, in the acceptor stem, D stem and anticodon stem respectively, are conversions of genomic cytidines to thymidines in the cDNA (uridines in the tRNA) and thus resemble the RNA editing events observed in nearly all plant mitochondrial mRNAs. Two cases of editing affecting mitochondrial tRNAs from angiosperms have already been described, but we present here the first example of such events in a gymnosperm mitochondrial tRNA. All three editing events correct mismatched C x A base pairs which appear when folding the gene sequence into the standard cloverleaf structure, thereby improving the secondary structure of the tRNA. When incubated with a heterologous potato mitochondrial processing extract, only the edited form of the larch mitochondrial tRNAHis precursor was efficiently processed in vitro. These data strongly suggest that editing of larch mitochondrial tRNAHis is a prerequisite for its processing.
落叶松线粒体含有一种被子植物所没有的“天然”组氨酰tRNA。对从编码该tRNA的落叶松线粒体基因trnH的未加工初级转录本中获得的基因组DNA和cDNA进行序列比较，发现了三个核苷酸差异。这三个核苷酸改变分别位于受体茎、D茎和反密码子茎中，是基因组胞嘧啶在cDNA中转变为胸腺嘧啶（tRNA中的尿嘧啶），因此类似于几乎所有植物线粒体mRNA中观察到的RNA编辑事件。已经描述了两例影响被子植物线粒体tRNA的编辑情况，但我们在此展示了裸子植物线粒体tRNA中此类事件的首个例子。所有这三个编辑事件都纠正了将基因序列折叠成标准三叶草结构时出现的错配C×A碱基对，从而改善了tRNA的二级结构。当与异源马铃薯线粒体加工提取物一起孵育时，体外仅落叶松线粒体tRNAHis前体的编辑形式能被有效加工。这些数据有力地表明，落叶松线粒体tRNAHis的编辑是其加工的先决条件。
