Hancock K, Hajduk S L
Department of Biochemistry, School of Medicine, University of Alabama, Birmingham 35294.
J Biol Chem. 1990 Nov 5;265(31):19208-15.
The mitochondrial DNA of Trypanosoma brucei is organized as a catenated network of maxicircles and minicircles. The maxicircles are equivalent to the typical mitochondrial genome except that the genes for the mitochondrial tRNAs have not been identified by sequence analysis of the maxicircle DNA. The apparent absence of tRNA genes in the maxicircle DNA suggests that the mitochondrial tRNAs are encoded by either the minicircle or the nuclear DNA. In order to determine their genomic origin, we isolated and identified the mitochondrial tRNAs of T. brucei. We show that these mitochondrial tRNAs are truly mitochondrially located in vivo and that they are free from detectable contamination by cytosolic RNAs. By hybridization analysis, using mitochondrial tRNAs as the probe, we determined that the mitochondrial tRNAs are encoded by nuclear DNA. This implies that RNAs, like proteins, are imported into the mitochondria. We investigated the relationship between the cytosolic and the mitochondrial tRNA genes and show that there are unique cytosolic tRNA genes, unique mitochondrial tRNA genes, and tRNA genes which appear to be shared and whose products are therefore targeted to both the cytosol and the mitochondrion.
布氏锥虫的线粒体DNA以由大圆环和小圆环组成的连环网络形式存在。大圆环相当于典型的线粒体基因组，只是通过大圆环DNA的序列分析尚未鉴定出线粒体tRNA的基因。大圆环DNA中明显不存在tRNA基因，这表明线粒体tRNA要么由小圆环编码，要么由核DNA编码。为了确定它们的基因组来源，我们分离并鉴定了布氏锥虫的线粒体tRNA。我们发现这些线粒体tRNA在体内确实定位于线粒体，并且未受到可检测到的胞质RNA污染。通过以线粒体tRNA为探针的杂交分析，我们确定线粒体tRNA由核DNA编码。这意味着RNA与蛋白质一样，是被导入线粒体的。我们研究了胞质tRNA基因与线粒体tRNA基因之间的关系，发现存在独特的胞质tRNA基因、独特的线粒体tRNA基因，以及似乎共享的tRNA基因，其产物因此靶向胞质溶胶和线粒体。
