Vanácová Stepánka, Yan Weihong, Carlton Jane M, Johnson Patricia J
Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 2005 Mar 22;102(12):4430-5. doi: 10.1073/pnas.0407500102. Epub 2005 Mar 11.
Eukaryotes have evolved elaborate splicing mechanisms to remove introns that would otherwise destroy the protein-coding capacity of genes. Nuclear premRNA splicing requires sequence motifs in the intron and is mediated by a ribonucleoprotein complex, the spliceosome. Here we demonstrate the presence of a splicing apparatus in the protist Trichomonas vaginalis and show that RNA motifs found in yeast and metazoan introns are required for splicing. We also describe the first introns in this deep-branching lineage. The positions of these introns are often conserved in orthologous genes, indicating they were present in a common ancestor of trichomonads, yeast, and metazoa. All examined T. vaginalis introns have a highly conserved 12-nt 3' splice-site motif that encompasses the branch point and is necessary for splicing. This motif is also found in the only described intron in a gene from another deep-branching eukaryote, Giardia intestinalis. These studies demonstrate the conservation of intron splicing signals across large evolutionary distances, reveal unexpected motif conservation in deep-branching lineages that suggest a simplified mechanism of splicing in primitive unicellular eukaryotes, and support the presence of introns in the earliest eukaryote.
真核生物已经进化出复杂的剪接机制来去除内含子，否则这些内含子会破坏基因的蛋白质编码能力。核前体mRNA剪接需要内含子中的序列基序，并由核糖核蛋白复合物剪接体介导。在这里，我们证明了原生生物阴道毛滴虫中存在剪接装置，并表明酵母和后生动物内含子中发现的RNA基序是剪接所必需的。我们还描述了这个进化分支较深的谱系中的首个内含子。这些内含子的位置在直系同源基因中通常是保守的，这表明它们存在于滴虫、酵母和后生动物的共同祖先中。所有检测的阴道毛滴虫内含子都有一个高度保守的12个核苷酸的3'剪接位点基序，该基序包含分支点，是剪接所必需的。这个基序也存在于另一种进化分支较深的真核生物——肠道贾第虫的一个基因中唯一描述的内含子中。这些研究证明了内含子剪接信号在大的进化距离上的保守性，揭示了进化分支较深的谱系中意想不到的基序保守性，这表明原始单细胞真核生物中存在简化的剪接机制，并支持最早的真核生物中存在内含子。
