Bullerwell Charles E, Schnare Murray N, Gray Michael W
Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada.
RNA. 2003 Mar;9(3):287-92. doi: 10.1261/rna.2170803.
Although 5S rRNA is a highly conserved and universal component of eubacterial, archaeal, chloroplast, and eukaryotic cytoplasmic ribosomes, a mitochondrial DNA-encoded 5S rRNA has so far been identified only in land plants and certain protists. This raises the question of whether 5S rRNA is actually required for and used in mitochondrial translation. In the protist Acanthamoeba castellanii, BLAST searches fail to reveal a 5S rRNA gene in the complete mitochondrial genome sequence, nor is a 5S-sized RNA species detectable in ethidium bromide-stained gels of highly purified mitochondrial RNA preparations. Here we show that an alternative visualization technique, UV shadowing, readily detects a novel, mitochondrion-specific small RNA in A. castellanii mitochondrial RNA preparations, and that this RNA species is, in fact, a 5S rRNA encoded by the A. castellanii mitochondrial genome. These results emphasize the need for caution when interpreting negative results that suggest the absence of 5S rRNA and/or a mitochondrial DNA-encoded 5S rRNA sequence in other (particularly protist) mitochondrial systems.
尽管5S核糖体RNA是真细菌、古细菌、叶绿体和真核细胞质核糖体中高度保守且普遍存在的组分，但线粒体DNA编码的5S核糖体RNA迄今仅在陆地植物和某些原生生物中被鉴定出来。这就引发了一个问题，即5S核糖体RNA在实际上是否是线粒体翻译所必需的以及是否被用于线粒体翻译。在原生生物卡氏棘阿米巴中，通过BLAST搜索未能在完整的线粒体基因组序列中发现5S核糖体RNA基因，在经溴化乙锭染色的高度纯化的线粒体RNA制剂凝胶中也检测不到5S大小的RNA种类。在此我们表明，一种替代性的可视化技术——紫外线阴影法，能轻易地在卡氏棘阿米线粒体RNA制剂中检测到一种新的、线粒体特异性小RNA，并且这种RNA种类实际上是由卡氏棘阿米线粒体基因组编码的5S核糖体RNA。这些结果强调，在解释那些表明其他（特别是原生生物）线粒体系统中不存在5S核糖体RNA和/或线粒体DNA编码的5S核糖体RNA序列的阴性结果时需要谨慎。
