McWatters David C, Russell Anthony G
Department of Biological Sciences, University of Lethbridge, 4401 University Dr W, Lethbridge, AB, Canada, T1K 6T5.
Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge, AB, Canada.
Adv Exp Med Biol. 2017;979:141-158. doi: 10.1007/978-3-319-54910-1_8.
RNA transcript processing is an important stage in the gene expression pathway of all organisms and is subject to various mechanisms of control that influence the final levels of gene products. RNA processing involves events such as nuclease-mediated cleavage, removal of intervening sequences referred to as introns and modifications to RNA structure (nucleoside modification and editing). In Euglena, RNA transcript processing was initially examined in chloroplasts because of historical interest in the secondary endosymbiotic origin of this organelle in this organism. More recent efforts to examine mitochondrial genome structure and RNA maturation have been stimulated by the discovery of unusual processing pathways in other Euglenozoans such as kinetoplastids and diplonemids. Eukaryotes containing large genomes are now known to typically contain large collections of introns and regulatory RNAs involved in RNA processing events, and Euglena gracilis in particular has a relatively large genome for a protist. Studies examining the structure of nuclear genes and the mechanisms involved in nuclear RNA processing have revealed that indeed Euglena contains large numbers of introns in the limited set of genes so far examined and also possesses large numbers of specific classes of regulatory and processing RNAs, such as small nucleolar RNAs (snoRNAs). Most interestingly, these studies have also revealed that Euglena possesses novel processing pathways generating highly fragmented cytosolic ribosomal RNAs and subunits and non-conventional intron classes removed by unknown splicing mechanisms. This unexpected diversity in RNA processing pathways emphasizes the importance of identifying the components involved in these processing mechanisms and their evolutionary emergence in Euglena species.
RNA转录本加工是所有生物体基因表达途径中的一个重要阶段，并且受到多种调控机制的影响，这些机制会影响基因产物的最终水平。RNA加工涉及核酸酶介导的切割、去除被称为内含子的间隔序列以及对RNA结构的修饰（核苷修饰和编辑）等事件。在眼虫中，由于历史上对该生物体中这种细胞器的次生内共生起源感兴趣，最初是在叶绿体中研究RNA转录本加工的。最近，由于在其他动基体目生物和双滴虫目生物等其他眼虫类中发现了不寻常的加工途径，人们对研究线粒体基因组结构和RNA成熟的兴趣受到了激发。现在已知含有大基因组的真核生物通常包含大量参与RNA加工事件的内含子和调控RNA，特别是纤细眼虫对于原生生物来说具有相对较大的基因组。对核基因结构以及核RNA加工所涉及机制的研究表明，在目前已研究的有限基因集中，眼虫确实含有大量内含子，并且还拥有大量特定类别的调控和加工RNA，如小核仁RNA（snoRNA）。最有趣的是，这些研究还表明，眼虫拥有产生高度片段化的胞质核糖体RNA及其亚基的新加工途径，以及通过未知剪接机制去除的非常规内含子类。RNA加工途径中这种意想不到的多样性强调了识别参与这些加工机制的成分及其在眼虫物种中的进化出现的重要性。
