Kamikawa Ryoma, Inagaki Yuji, Hashimoto Tetsuo
Center for Computational Sciences and Institute of Biological Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8577, Japan.
Biophys Rev. 2011 Dec;3(4):193-197. doi: 10.1007/s12551-011-0058-3. Epub 2011 Oct 20.
Although spliceosomal introns are an abundant landmark in eukaryotic genomes, the nuclear genome of the divergent eukaryote Giardia intestinalis, the causative agent of giardiasis, has been considered as "intron-poor" with only five canonical (cis-spliced) introns. However, three research groups (including ours) have independently reported a novel class of spliceosomal introns in the G. intestinalis genome. Three protein-coding genes are split into pieces in the G. intestinalis genome, and each of the partial coding regions was independently transcribed into polyadenylated premature mRNAs (pre-mRNAs). The two pre-mRNAs directly interact with each other by an intermolecular-stem structure formed between their non-coding portions, and are then processed into mature mRNAs by spliceosome-mediated trans-splicing. Here, we summarize the recently published works on split introns ("splintrons") in the G. intestinalis genome, and then provide our speculation on the functional property of the Giardia spliceosomes based on the putative ratio of splintrons to canonical introns. Finally, we discuss a scenario for the transition from typical GT-AG boundaries to non-typical AT-AC boundaries in a particular splintron of Giardia.
尽管剪接体内含子是真核生物基因组中丰富的标志性特征，但引起贾第虫病的真核生物——贾第鞭毛虫的核基因组，被认为是“内含子贫乏”的，仅含有五个典型（顺式剪接）内含子。然而，三个研究小组（包括我们的小组）独立报道了贾第鞭毛虫基因组中一类新型的剪接体内含子。在贾第鞭毛虫基因组中，三个蛋白质编码基因被分割成片段，每个部分编码区域都独立转录为聚腺苷酸化的前体mRNA（pre-mRNA）。这两个前体mRNA通过它们非编码部分之间形成的分子间茎结构直接相互作用，然后通过剪接体介导的反式剪接加工成成熟的mRNA。在这里，我们总结了最近发表的关于贾第鞭毛虫基因组中分裂内含子（“夹板内含子”）的研究工作，然后基于夹板内含子与典型内含子的假定比例，对贾第虫剪接体的功能特性进行推测。最后，我们讨论了在贾第虫的一个特定夹板内含子中从典型的GT-AG边界向非典型的AT-AC边界转变的一种情况。
