A spliceosomal intron in Giardia lamblia
A spliceosomal intron in Giardia lamblia
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DOI：
10.1073/pnas.042700299
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发表时间：
2002-03-19
影响因子：
11.1
通讯作者：
Samuelson, J
中科院分区：
文献类型：
--
作者：
Nixon, JEJ;Wang, A;Samuelson, J
短内含子出现在许多原生生物谱系中，但没有在原生生物兰第鞭毛虫和阴道毛滴虫中发现介入序列的报道，这可能是真核生物谱系中已知最深的分支。我们发现了一个35-bp剪接体内的内含子在一个基因编码一个假定的[2Fe-2S]铁还原蛋白的蓝氏螺旋体。贾第鞭毛虫内含子在其3‘端包含一个典型剪接位点（AG），在其5’端包含一个非典型剪接位点（CT），除了第一个核苷酸（AACTAAC）外，分支点序列与酵母菌的TACTAAC一致序列吻合。我们还发现了几种具有剪接体肽的兰氏杆菌基因，包括真核特异性剪接体肽的同源物（Prp8和Prp11），几种在真核生物中具有同源物的DExH-box rna解旋酶，但在真核生物的内含子剪接中起重要作用，以及11种预测古细菌样Sm和样Sm核心肽，这些核心肽包裹着小核rna。系统发育分析表明，贾第鞭毛虫Sm核心肽是祖先基因多次复制和分化的产物，但它们与其他真核生物的Sm和类Sm肽具有很强的相似性。虽然我们在贾第鞭毛虫中只记录了一个内含子，但它可能有其他内含子和功能齐全的剪接体机制。如果内含子是在真核生物进化过程中添加的（内含子晚期假说），那么这些结果将这一事件的日期推迟到G. lamblia分支之前。
Short introns occur in numerous protist lineages, but there are no reports of intervening sequences in the protists Giardia lamblia and Trichomonas vaginalis, which may represent the deepest known branches in the eukaryotic line of descent. We have discovered a 35-bp spliceosomal intron in a gene encoding a putative [2Fe-2S] ferredoxin of G. lamblia. The Giardia intron contains a canonical splice site at its 3' end (AG), a noncanonical splice site at its 5' end (CT), and a branch point sequence that fits the yeast consensus sequence of TACTAAC except for the first nucleotide (AACTAAC). We have also identified several G. lamblia genes with spliceosomal peptides, including homologues of eukaryote-specific spliceosomal peptides (Prp8 and Prp11), several DExH-box RNA-helicases that have homologues in eubacteria, but serve essential functions in the splicing of introns in eukaryotes, and 11 predicted archae-bacteria-like Sm and like-Sm core peptides, which coat small nuclear RNAs. Phylogenetic analyses show the Giardia Sm core peptides are the products of multiple, ancestral gene duplications followed by divergence, but they retain strong similarity to Sm and like-Sm peptides of other eukaryotes. Although we have documented only a single intron in Giardia, it likely has other introns and fully functional, spliceosomal machinery. If introns were added during eukaryotic evolution (the introns-late hypothesis), then these results push back the date of this event before the branching of G. lamblia.