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Unusual features of fibrillarin cDNA and gene structure in Euglena gracilis: evolutionary conservation of core proteins and structural predictions for methylation-guide box C/D snoRNPs throughout the domain Eucarya

机译:Euglena gracilis中原纤维蛋白cDNA的异常特征和基因结构:核心蛋白的进化保守性和整个Eucarya区域甲基化指导盒C / D snoRNPs的结构预测

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摘要

Box C/D ribonucleoprotein (RNP) particles mediate O2′-methylation of rRNA and other cellular RNA species. In higher eukaryotic taxa, these RNPs are more complex than their archaeal counterparts, containing four core protein components (Snu13p, Nop56p, Nop58p and fibrillarin) compared with three in Archaea. This increase in complexity raises questions about the evolutionary emergence of the eukaryote-specific proteins and structural conservation in these RNPs throughout the eukaryotic domain. In protists, the primarily unicellular organisms comprising the bulk of eukaryotic diversity, the protein composition of box C/D RNPs has not yet been extensively explored. This study describes the complete gene, cDNA and protein sequences of the fibrillarin homolog from the protozoon Euglena gracilis, the first such information to be obtained for a nucleolus-localized protein in this organism. The E.gracilis fibrillarin gene contains a mixture of intron types exhibiting markedly different sizes. In contrast to most other E.gracilis mRNAs characterized to date, the fibrillarin mRNA lacks a spliced leader (SL) sequence. The predicted fibrillarin protein sequence itself is unusual in that it contains a glycine-lysine (GK)-rich domain at its N-terminus rather than the glycine-arginine-rich (GAR) domain found in most other eukaryotic fibrillarins. In an evolutionarily diverse collection of protists that includes E.gracilis, we have also identified putative homologs of the other core protein components of box C/D RNPs, thereby providing evidence that the protein composition seen in the higher eukaryotic complexes was established very early in eukaryotic cell evolution.
机译:Box C / D核糖核蛋白(RNP)颗粒介导rRNA和其他细胞RNA物种的O2'-甲基化。在高等真核生物类群中,这些RNP比其古细菌对应物更为复杂,包含四个核心蛋白成分(Snu13p,Nop56p,Nop58p和原纤维蛋白),而古细菌中则为三个。这种复杂性的增加提出了关于真核生物特异性蛋白的进化出现以及这些RNP在整个真核域中的结构保守性的问题。在存在大量真核生物多样性的主要是单细胞生物的原生生物中,框C / D RNPs的蛋白质组成尚未得到广泛研究。这项研究描述了原虫Euglena gracilis的原纤维蛋白同源物的完整基因,cDNA和蛋白质序列,这是该生物中首个定位于核仁的蛋白质的信息。细粒肠杆菌纤丝蛋白基因包含大小不同的内含子类型的混合物。与迄今表征的大多数其他细小芽孢杆菌mRNA相比,原纤维蛋白mRNA缺乏剪接的前导序列(SL)。预测的纤维蛋白原蛋白序列本身是不寻常的,因为它在其N端包含一个富含甘氨酸-赖氨酸(GK)的域,而不是在大多数其他真核纤维蛋白原中发现的富含甘氨酸-精氨酸的(GAR)域。在进化多样的包括细粒肠杆菌的原生生物的集合中,我们还鉴定了框C / D RNPs其他核心蛋白质成分的推定同源物,从而提供了证据,证明在高等真核复合物中看到的蛋白质组成是在很早的时候就建立的。真核细胞进化。

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