Blom D, de Haan A, van den Berg M, Sloof P, Jirku M, Lukes J, Benne R
Department of Biochemistry/AMC, University of Amsterdam, Academic Medical Centre, Meibergdreef 15, 1105 AZ, Amsterdam, The Netherlands.
Nucleic Acids Res. 1998 Mar 1;26(5):1205-13. doi: 10.1093/nar/26.5.1205.
In parasitic kinetoplastid protozoa, mitochondrial (mt) mRNAs are post-transcriptionally edited by insertion and deletion of uridylate residues, the information being provided by guide (g) RNAs. In order to further explore the role and evolutionary history of this process, we searched for editing in mt RNAs of the free-living bodonid Bodo saltans. We found extensive editing in the transcript for NADH dehydrogenase (ND) subunit 5, which is unedited in trypanosomatids. In contrast, B.saltans cytochrome c oxidase (cox) subunit 2 and maxicircle unidentified reading frame (MURF) 2 RNAs display limited editing in the same regions as their trypanosomatid counterparts. A putative intramolecular cox2 gRNA and the gene for gMURF2-I directing the insertion of only one U in the 5' editing domain of MURF2 RNA, are conserved in B.saltans. This lends (further) evolutionary support to the proposed role of these sequences as gRNAs. Phylogenetic analysis showed that B.saltans is more closely related to trypanosomatids than the cryptobiids Trypanoplasma borreli and Cryptobia helicis, in line with the trypanosomatid-like cox2 and MURF2 RNA editing patterns. Nevertheless, other features like the apparent absence of a catenated mtDNA network, are shared with bodonid and cryptobiid species. ND5 RNA editing may represent yet another example of editing 'on the way out' during kinetoplastid evolution, but in view of the fact that cox2 RNA is unedited in T. borreli and C.helicis, we infer that the editing of this RNA may have arisen relatively recently. Our results provide the first examples of RNA editing in a free-living kinetoplastid, indicating that there is no direct link between U-insertion/deletion editing and a parasitic lifestyle.
在寄生性动质体原生动物中，线粒体（mt）mRNA通过尿苷酸残基的插入和缺失进行转录后编辑，其信息由引导（g）RNA提供。为了进一步探索这一过程的作用和进化历史，我们在自由生活的波豆虫属盐沼波豆虫（Bodo saltans）的mt RNA中寻找编辑情况。我们发现烟酰胺腺嘌呤二核苷酸脱氢酶（ND）亚基5的转录本存在广泛编辑，而在锥虫中该转录本未被编辑。相比之下，盐沼波豆虫细胞色素c氧化酶（cox）亚基2和大环未鉴定阅读框（MURF）2 RNA在与它们锥虫对应物相同的区域显示出有限的编辑。一个推定的分子内cox2 gRNA和指导在MURF2 RNA的5'编辑结构域仅插入一个U的gMURF2 - I基因，在盐沼波豆虫中是保守的。这为这些序列作为gRNA的假定作用提供了（进一步的）进化支持。系统发育分析表明，盐沼波豆虫与锥虫的关系比隐鞭毛虫类的博氏锥虫（Trypanoplasma borreli）和螺旋隐鞭虫（Cryptobia helicis）更密切，这与类似锥虫的cox2和MURF2 RNA编辑模式一致。然而，其他特征如明显不存在连环的mtDNA网络，则与波豆虫属和隐鞭毛虫类物种共有。ND5 RNA编辑可能代表动质体进化过程中“逐渐消失”的编辑的又一个例子，但鉴于cox2 RNA在博氏锥虫和螺旋隐鞭虫中未被编辑这一事实，我们推断该RNA的编辑可能是相对较近才出现的。我们的结果提供了自由生活的动质体中RNA编辑的首个例子，表明尿苷酸插入/缺失编辑与寄生生活方式之间没有直接联系。
