Lambowitz Alan M, Zimmerly Steven
Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry, Section of Molecular Genetics and Microbiology, University of Texas at Austin, Texas 78712, USA.
Annu Rev Genet. 2004;38:1-35. doi: 10.1146/annurev.genet.38.072902.091600.
Mobile group II introns, found in bacterial and organellar genomes, are both catalytic RNAs and retrotransposable elements. They use an extraordinary mobility mechanism in which the excised intron RNA reverse splices directly into a DNA target site and is then reverse transcribed by the intron-encoded protein. After DNA insertion, the introns remove themselves by protein-assisted, autocatalytic RNA splicing, thereby minimizing host damage. Here we discuss the experimental basis for our current understanding of group II intron mobility mechanisms, beginning with genetic observations in yeast mitochondria, and culminating with a detailed understanding of molecular mechanisms shared by organellar and bacterial group II introns. We also discuss recently discovered links between group II intron mobility and DNA replication, new insights into group II intron evolution arising from bacterial genome sequencing, and the evolutionary relationship between group II introns and both eukaryotic spliceosomal introns and non-LTR-retrotransposons. Finally, we describe the development of mobile group II introns into gene-targeting vectors, "targetrons," which have programmable target specificity.
移动II组内含子存在于细菌和细胞器基因组中，它们既是催化性RNA，又是反转录转座元件。它们采用一种独特的移动机制，即切除的内含子RNA直接反向剪接到DNA靶位点，然后由内含子编码的蛋白质进行反转录。DNA插入后，内含子通过蛋白质辅助的自催化RNA剪接将自身去除，从而将对宿主的损害降至最低。在这里，我们将讨论目前对II组内含子移动机制理解的实验基础，从酵母线粒体中的遗传学观察开始，最终深入了解细胞器和细菌II组内含子共有的分子机制。我们还将讨论最近发现的II组内含子移动与DNA复制之间的联系、细菌基因组测序对II组内含子进化的新见解，以及II组内含子与真核剪接体内含子和非LTR反转录转座子之间的进化关系。最后，我们描述了移动II组内含子发展成为具有可编程靶标特异性的基因靶向载体“靶标子”的过程。
