Malek O, Brennicke A, Knoop V
Allgemeine Botanik, Universität Ulm, Germany.
Proc Natl Acad Sci U S A. 1997 Jan 21;94(2):553-8. doi: 10.1073/pnas.94.2.553.
Trans-splicing in angiosperm plant mitochondria connects exons from independent RNA molecules by means of group II intron fragments. Homologues of trans-splicing introns in the angiosperm mitochondrial nad2 and nad5 genes are now identified as uninterrupted group II introns in the ferns Asplenium nidus and Marsilea drummondii. These fern introns are correctly spliced from the pre-mRNA at the sites predicted from their well-conserved secondary structures. The flanking exon sequences of the nad2 and nad5 genes in the ferns require RNA editing, including the removal of in-frame stop codons by U-to-C changes for correct expression of the genetic information. We conclude that cis-splicing introns like the ones now identified in ferns are the ancestors of trans-splicing introns in angiosperm mitochondria. Intron disruption is apparently due to a size increase of the structurally variable group II intron domain IV followed by DNA recombination in the plant mitochondrial genome.
被子植物线粒体中的反式剪接通过II类内含子片段将独立RNA分子中的外显子连接起来。现在，在蕨类植物鸟巢蕨和鼓叶苹的线粒体中，被子植物线粒体nad2和nad5基因中的反式剪接内含子同源物被鉴定为不间断的II类内含子。这些蕨类植物内含子从其前体mRNA上的正确位置被剪接下来，这些位置是根据其高度保守的二级结构预测出来的。蕨类植物nad2和nad5基因的侧翼外显子序列需要进行RNA编辑，包括通过U到C的变化去除框内终止密码子，以正确表达遗传信息。我们得出结论，像现在在蕨类植物中鉴定出的顺式剪接内含子是被子植物线粒体中反式剪接内含子的祖先。内含子的中断显然是由于结构可变的II类内含子结构域IV的大小增加，随后在植物线粒体基因组中发生了DNA重组。
