Center for Computational Sciences and Institute of Biological Sciences, University of Tsukuba, Ibaraki 305-8577, Japan.
Curr Biol. 2011 Feb 22;21(4):311-5. doi: 10.1016/j.cub.2011.01.025.
Spliceosomal introns are hallmarks of most eukaryotic genomes and are excised from premature mRNAs by a spliceosome that is among the largest, and most complex, molecular machine in cells. The divergent unicellular eukaryote Giardia intestinalis, the causative agent of giardiasis, also possesses spliceosomes, but only four canonical (cis-spliced) introns have been identified in its genome to date. We demonstrate that this organism has a novel form of spliceosome-mediated trans-splicing of split introns that is essential for generating mature mRNAs for at least two important genes: one encoding a heat shock protein 90 (HSP90), which controls the conformation of a suite of cellular proteins, and the other encoding a dynein molecular motor protein, involved in the motility of eukaryotic flagella. These split introns have properties that distinguish them from other trans-splicing systems known within eukaryotes, suggesting that Giardia independently evolved a unique system to splice split introns.
剪接体内含子是大多数真核生物基因组的特征，通过剪接体从不成熟的 mRNA 中切除，剪接体是细胞中最大、最复杂的分子机器之一。具有分歧的单细胞真核生物贾第虫（引起贾第虫病的病原体）也拥有剪接体，但迄今为止，其基因组中仅鉴定出了四个典型的（顺式剪接）内含子。我们证明，该生物体具有一种新型的剪接体介导的分裂内含子的反式剪接，这对于生成至少两个重要基因的成熟 mRNA 是必不可少的：一个基因编码热休克蛋白 90（HSP90），它控制着一套细胞蛋白的构象，另一个基因编码动力蛋白分子马达蛋白，参与真核鞭毛的运动。这些分裂内含子具有将它们与真核生物中已知的其他反式剪接系统区分开来的特性，表明贾第虫独立进化出了一种独特的剪接分裂内含子的系统。
