Ⅱ组内含子(Group Ⅱ Introns)的分布及多样性

Distribution and Diversity of Group Ⅱ Introns

Ⅱ组内含子(groupⅡintron)存在于原生生物、真菌、藻类、植物细胞器以及细菌和古细菌基因组中.在体内,Ⅱ组内含子可通过两步连续的转酯反应从前体RNA中自剪接,并连接两侧外显子.许多Ⅱ组内含子的剪接反应是由蛋白质辅助完成的,这种蛋白质有的是由内含子编码,有的是由宿主基因编码.Ⅱ组内含子能够有效地归巢进入无内含子的等位基因,也能够以低频率逆转座进入非等位基因.转座过程依赖内含子RNA和内含子编码的蛋白质(内切核酸酶活性和逆转录酶活性).本论文在总结Ⅱ组内含子最新研究成果的基础上,分析Ⅱ组内含子可能的起源和进化途径.

Group Ⅱ introns are found in mitochondria and chloroplasts genomes of plants, fungi, protists and algae, as well as bacterial and arehaebacterial genomes. In intracellular organelles, group Ⅱ introns are typically found in highly conserved genes, whereas the bacterial groupⅡ introns are mainly located in mobile DNAs which are carrying non-conserved genes, except the recent discovery of the presence of group Ⅱ introns in some conserved bacterial genome coding regions. By far, none of the archael group Ⅱ introns are reported in the cellular genes of their hosts. In living cells, some of the group Ⅱ introns were found to self-splice from their pre-RNAs following two consecutive transesterification reactions, then join the flanking exons and release the intron in a typical lariat form. The splicing reactions of many, not all group Ⅱintrons are assisted by proteins encoded by either the introns themselves, or other genes of the host organisms. Group Ⅱ introns can integrate efficiently into intronless alleles of the same gene or at much lower frequencies into ectopic sites. The mobility of group Ⅱ introns depends on the functions of intron encoded proteins （endonuclease and reverse transcriptase） and the RNA sequence and structure of the introns. In this article, we intend to give an overview about the recent research progress and insights of group Ⅱ introns. The diversity, origin and evolution of group Ⅱ introns will be primarily focused.