Hong Y, Dover S L, Cole T E, Brasier C M, Buck K W
Department of Biology, Imperial College of Science, Technology and Medicine, Imperial College Road, London, SW7 2AZ, United Kingdom.
Virology. 1999 May 25;258(1):118-27. doi: 10.1006/viro.1999.9691.
The nucleotide sequences of three mitochondrial virus double-stranded (ds) RNAs, RNA-4 (2599 nucleotides), RNA-5 (2474 nucleotides), and RNA-6 (2343 nucleotides), in a diseased isolate Log1/3-8d2 (Ld) of the Dutch elm disease fungus Ophiostoma novo-ulmi have been determined. All these RNAs are A-U-rich (71-73% A + U residues). Using the fungal mitochondrial genetic code in which UGA codes for tryptophan, the positive-strand of each of RNAs 4, 5, and 6 contains a single open reading frame (ORF) with the potential to encode a protein of 783, 729, and 695 amino acids, respectively, all of which contain conserved motifs characteristic of RNA-dependent RNA polymerases (RdRps). Sequence comparisons showed that these RNAs are related to each other and to a previously characterized RNA, RNA-3a, from the same O. novo-ulmi isolate, especially within the RdRp-like motifs. However, the overall RNA nucleotide and RdRp amino acid sequence identities were relatively low (43-55% and 20-32%, respectively). The 5'- and 3'-terminal sequences of these RNAs are different, but they can all be folded into potentially stable stem-loop structures. Those of RNA-4 and RNA-6 have inverted complementarity, potentially forming panhandle structures. Their molecular and biological properties indicate that RNAs 3a, 4, 5, and 6 are the genomes of four different viruses, which replicate independently in the same cell. These four viruses are also related to a mitochondrial RNA virus from another fungus, Cryphonectria parasitica, recently designated the type species of the Mitovirus genus of the Narnaviridae family, and to a virus from the fungus Rhizoctonia solani. It is proposed that the four O. novo-ulmi mitochondrial viruses are assigned to the Mitovirus genus and designated O. novo-ulmi mitovirus (OnuMV) 3a-Ld, 4-Ld, 5-Ld, and 6-Ld, respectively. Northern blot analysis indicated that O. novo-ulmi Ld nucleic acid extracts contain more single-stranded (ss, positive-stranded) RNA than dsRNA for all three newly described mitoviruses. O. novo-ulmi RNA-7, previously believed to be a satellite-like RNA, is shown to be a defective RNA, derived from OnuMV4-Ld RNA by multiple internal deletions. OnuMV4-Ld is therefore the helper virus for the replication of both RNA-7 and another defective RNA, RNA-10. Sequence comparisons indicate that RNA-10 could be derived from RNA-7, as previously suggested, or derived directly from RNA-4.
已测定荷兰榆树病真菌新榆枯萎病菌（Ophiostoma novo-ulmi）患病分离株Log1/3-8d2（Ld）中三种线粒体病毒双链（ds）RNA，即RNA-4（2599个核苷酸）、RNA-5（2474个核苷酸）和RNA-6（2343个核苷酸）的核苷酸序列。所有这些RNA富含A-U（A + U残基占71 - 73%）。使用UGA编码色氨酸的真菌线粒体遗传密码，RNA 4、5和6的正链各自包含一个单一开放阅读框（ORF），分别有可能编码783、729和695个氨基酸的蛋白质，所有这些蛋白质都含有RNA依赖性RNA聚合酶（RdRps）的保守基序。序列比较表明，这些RNA彼此相关，并且与来自同一新榆枯萎病菌分离株的先前已鉴定的RNA - 3a相关，特别是在RdRp样基序内。然而，总体RNA核苷酸和RdRp氨基酸序列同一性相对较低（分别为43 - 55%和20 - 32%）。这些RNA的5'和3'末端序列不同，但它们都可以折叠成潜在稳定的茎环结构。RNA - 4和RNA - 6的末端序列具有反向互补性，有可能形成锅柄结构。它们的分子和生物学特性表明，RNA 3a、4、5和6是四种不同病毒的基因组，它们在同一细胞中独立复制。这四种病毒还与来自另一种真菌寄生隐孢壳菌（Cryphonectria parasitica）的线粒体RNA病毒相关，该病毒最近被指定为纳马病毒科（Narnaviridae）线粒体病毒属的模式种，并且与来自真菌立枯丝核菌（Rhizoctonia solani）的一种病毒相关。建议将这四种新榆枯萎病菌线粒体病毒分别归入线粒体病毒属，并分别命名为新榆枯萎病菌线粒体病毒（OnuMV）3a - Ld、4 - Ld、5 - Ld和6 - Ld。Northern印迹分析表明，对于所有三种新描述的线粒体病毒，新榆枯萎病菌Ld核酸提取物中含有的单链（ss，正链）RNA比dsRNA更多。新榆枯萎病菌RNA - 7以前被认为是一种类卫星RNA，现被证明是一种缺陷RNA，由OnuMV4 - Ld RNA通过多次内部缺失产生。因此，OnuMV4 - Ld是RNA -
