Daley Daniel O, Adams Keith L, Clifton Rachel, Qualmann Svenja, Millar A Harvey, Palmer Jeffrey D, Pratje Elke, Whelan James
Department of Biochemistry, University of Western Australia, Nedlands 6907, Australia.
Plant J. 2002 Apr;30(1):11-21. doi: 10.1046/j.1365-313x.2002.01263.x.
The evolutionarily recent transfer of the gene for cytochrome c oxidase subunit 2 (cox2) from the mitochondrion to the nucleus in legumes is shown to have involved novel gene-activation steps. The acquired mitochondrial targeting presequence is bordered by two introns. Characterization of the import of soybean Cox2 indicates that the presequence is cleaved in a three-step process which is independent of assembly. The final processing step takes place only in the mitochondria of legume species, and not in several non-legume plants. The unusually long presequence of 136 amino acids consists of three regions: the first 20 amino acids are required for mitochondrial targeting and can be replaced by another presequence; the central portion of the presequence is required for efficient import of the Cox2 protein into mitochondria; and the last 12 amino acids, derived from the mitochondrially encoded protein, are required for correct maturation of the imported protein. The acquisition of a unique presequence, and the capacity for legume mitochondria to remove this presequence post-import, are considered to be essential adaptations for targeting of Cox2 to the mitochondrion and therefore activation of the transferred gene in the nucleus.
研究表明，豆科植物中细胞色素c氧化酶亚基2（cox2）基因从线粒体到细胞核的进化上较新的转移涉及新的基因激活步骤。获得的线粒体靶向前序列由两个内含子界定。对大豆Cox2导入过程的表征表明，前序列在一个三步过程中被切割，该过程与组装无关。最后的加工步骤仅发生在豆科植物的线粒体中，而在几种非豆科植物中则不会发生。异常长的136个氨基酸的前序列由三个区域组成：前20个氨基酸是线粒体靶向所必需的，可以被另一个前序列取代；前序列的中央部分是Cox2蛋白有效导入线粒体所必需的；最后12个氨基酸源自线粒体编码的蛋白，是导入蛋白正确成熟所必需的。获得独特的前序列以及豆科植物线粒体在导入后去除该前序列的能力，被认为是将Cox2靶向线粒体并因此激活细胞核中转移基因的重要适应性特征。
