Zimmerly S, Hausner G
Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
Nucleic Acids Res. 2001 Mar 1;29(5):1238-50. doi: 10.1093/nar/29.5.1238.
Group II introns are widely believed to have been ancestors of spliceosomal introns, yet little is known about their own evolutionary history. In order to address the evolution of mobile group II introns, we have compiled 71 open reading frames (ORFs) related to group II intron reverse transcriptases and subjected their derived amino acid sequences to phylogenetic analysis. The phylogenetic tree was rooted with reverse transcriptases (RTs) of non-long terminal repeat retroelements, and the inferred phylogeny reveals two major clusters which we term the mitochondrial and chloroplast-like lineages. Bacterial ORFs are mainly positioned at the bases of the two lineages but with weak bootstrap support. The data give an overview of an apparently high degree of horizontal transfer of group II intron ORFs, mostly among related organisms but also between organelles and bacteria. The Zn domain (nuclease) and YADD motif (RT active site) were lost multiple times during evolution. Differences in domain structures suggest that the oldest ORFs were concise, while the ORF in the mitochondrial lineage subsequently expanded in three locations. The data are consistent with a bacterial origin for mobile group II introns.
人们普遍认为Ⅱ类内含子是剪接体内含子的祖先，但对其自身的进化历史却知之甚少。为了研究可移动Ⅱ类内含子的进化，我们收集了71个与Ⅱ类内含子逆转录酶相关的开放阅读框（ORF），并对其推导的氨基酸序列进行了系统发育分析。系统发育树以非长末端重复逆转录元件的逆转录酶（RT）为根，推断的系统发育揭示了两个主要的簇，我们将其称为线粒体和叶绿体样谱系。细菌的开放阅读框主要位于两个谱系的基部，但自展支持较弱。这些数据概述了Ⅱ类内含子开放阅读框明显高度的水平转移，主要发生在相关生物体之间，但也存在于细胞器和细菌之间。锌结构域（核酸酶）和YADD基序（逆转录酶活性位点）在进化过程中多次丢失。结构域结构的差异表明，最古老的开放阅读框很简洁，而线粒体谱系中的开放阅读框随后在三个位置扩展。这些数据与可移动Ⅱ类内含子起源于细菌的观点一致。
