Gray M W, Covello P S
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada.
FASEB J. 1993 Jan;7(1):64-71. doi: 10.1096/fasebj.7.1.8422976.
In the mitochondria and chloroplasts of flowering plants (angiosperms), transcripts of protein-coding genes are altered after synthesis so that their final primary nucleotide sequence differs from that of the corresponding DNA sequence. This posttranscriptional mRNA editing consists almost exclusively of C-to-U substitutions. Editing occurs predominantly within coding regions, mostly at isolated C residues, and usually at first or second positions of codons, thereby almost always changing the amino acid from that specified by the unedited codon. Editing may also create initiation and termination codons. The net effect of C-to-U RNA editing in plants is to make proteins encoded by plant organelles more similar in sequence to their nonplant homologs. In a few cases, a strong argument can be made that specific C-to-U editing events are essential for the production of functional plant mitochondrial proteins. Although the phenomenon of RNA editing in plants is now well documented, fundamental questions remain to be answered: What determines the specificity of editing? What is the biochemical mechanism (deamination, base exchange, or nucleotide replacement)? How did the system evolve? RNA editing in plants, as in other organisms, challenges our traditional notions of genetic information transfer.
在开花植物（被子植物）的线粒体和叶绿体中，蛋白质编码基因的转录本在合成后会发生改变，因此其最终的初级核苷酸序列与相应的DNA序列不同。这种转录后mRNA编辑几乎完全由C到U的替换组成。编辑主要发生在编码区域内，大多在孤立的C残基处，并且通常在密码子的第一位或第二位，从而几乎总是改变未编辑密码子所指定的氨基酸。编辑还可能产生起始密码子和终止密码子。植物中C到U的RNA编辑的净效应是使植物细胞器编码的蛋白质在序列上与其非植物同源物更相似。在少数情况下，可以有力地证明特定的C到U编辑事件对于功能性植物线粒体蛋白质的产生至关重要。尽管现在植物中的RNA编辑现象已有充分记录，但仍有一些基本问题有待解答：是什么决定了编辑的特异性？生化机制是什么（脱氨基、碱基交换还是核苷酸替换）？该系统是如何进化的？与其他生物一样，植物中的RNA编辑挑战了我们对遗传信息传递的传统观念。
