Okimoto R, Wolstenholme D R
Department of Biology, University of Utah, Salt Lake City 84112.
EMBO J. 1990 Oct;9(10):3405-11. doi: 10.1002/j.1460-2075.1990.tb07542.x.
The mitochondrial DNA (mtDNA) molecules of the nematode worms, Caenorhabditis elegans and Ascaris suum contain 22 putative genes for non-standard forms of tRNAs. The inferred transcripts can be folded into 20 separate structures each resembling a tRNA whose T psi C arm and variable loop are replaced with a simple loop of 6-12 nucleotides. In two further structures [that resemble tRNAs for ser(UCN) and ser(AGN)], the dihydrouridine arm is replaced by a loop of 5-8 nucleotides. By hybridizing mt-tRNA gene-specific oligonucleotide probes to nematode RNAs, we have obtained evidence for transcription of at least nine C.elegans and three A.suum mt-tRNA genes. Each transcript (tRNA) is the exact size predicted from the respective DNA sequence, to which three nucleotides, presumably CCA, have been added following transcription. An exception was C.elegans mt-tRNAasn, most molecules of which had one nucleotide (plus CCA) more than predicted from the gene. The data presented strongly support the conclusion that the functional mt-tRNAs of nematode worms are direct transcripts (with only CCA addition) of the structurally unusual mt-tRNA genes. There is no evidence of trans-splicing or RNA editing to add the sequences missing from these nonstandard tRNAs. We presume, therefore, that the non-standard forms are active in mitochondrial protein synthesis.
线虫秀丽隐杆线虫和猪蛔虫的线粒体DNA（mtDNA）分子含有22个推测的非标准形式tRNA的基因。推测的转录本可折叠成20个独立的结构，每个结构类似于一个tRNA，其TψC臂和可变环被一个6 - 12个核苷酸的简单环取代。在另外两个结构中（类似于ser（UCN）和ser（AGN）的tRNA），二氢尿嘧啶臂被一个5 - 8个核苷酸的环取代。通过将线粒体tRNA基因特异性寡核苷酸探针与线虫RNA杂交，我们获得了至少九个秀丽隐杆线虫和三个猪蛔虫线粒体tRNA基因转录的证据。每个转录本（tRNA）的大小与从各自DNA序列预测的完全一致，转录后添加了三个核苷酸，推测为CCA。秀丽隐杆线虫的线粒体tRNAasn是个例外，其大多数分子比基因预测的多一个核苷酸（加上CCA）。所呈现的数据有力地支持了这样的结论，即线虫的功能性线粒体tRNA是结构异常的线粒体tRNA基因的直接转录本（仅添加CCA）。没有证据表明存在转剪接或RNA编辑来添加这些非标准tRNA中缺失的序列。因此，我们推测这些非标准形式在线粒体蛋白质合成中是有活性的。
