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首页> 外文期刊>Molecular and Cellular Biology >Characterization of mutant mitochondrial plasmids of Neurospora spp. that have incorporated tRNAs by reverse transcription.
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Characterization of mutant mitochondrial plasmids of Neurospora spp. that have incorporated tRNAs by reverse transcription.

机译：Neurospora spp的突变线粒体质粒的表征。通过逆转录结合了tRNA的那些。

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The Mauriceville and Varkud mitochondrial plasmids of Neurospora spp. are closely related, closed-circular DNAs (3.6 and 3.7 kilobases, respectively) whose nucleotide sequences and genetic organization suggest relationships to mitochondrial introns and retroelements. We have characterized nine suppressive mutants of these plasmids that outcompete mitochondrial DNA and lead to impaired growth. All nine suppressive plasmids contain small insertions, corresponding to or including a mitochondrial tRNA (tRNATrp, tRNAGly, or tRNAVal) or a tRNA-like sequence. The insertions are located at the position corresponding to the 5' end of the major plasmid transcript or 24 nucleotides downstream near a cognate of the sequence at the major 5' RNA end. The structure of the suppressive plasmids suggests that the tRNAs were inserted via an RNA intermediate. The 3' end of the wild-type plasmid transcript can itself be folded into a secondary structure which has tRNA-like characteristics, similar to the tRNA-like structures at the 3' ends of plant viral RNAs. This structure may play a role in replication of the plasmids by reverse transcription. Major transcripts of the suppressive plasmids begin at the 5' end of the inserted mitochondrial tRNA sequence and are present in 25- to 100-fold-higher concentrations than are transcripts of wild-type plasmids. Mapping of 5' RNA ends within the inserted mtDNA sequences identifies a short consensus sequence (PuNPuAG) which is present at the 5' ends of a subset of mitochondrial tRNA genes. This sequence, together with sequences immediately upstream in the plasmids, forms a longer consensus sequence, which is similar to sequences at transcription initiation sites in Neurospora mitochondrial DNA. The suppressive behavior of the plasmids is likely to be directly related to the insertion of tRNAs leading to overproduction of plasmid transcripts.
机译：Neurospora spp的Mauriceville和Varkud线粒体质粒。是紧密相关的闭环DNA（分别为3.6和3.7千碱基），其核苷酸序列和遗传结构暗示与线粒体内含子和反转录元件的关系。我们已经表征了这些质粒的九种抑制性突变体，它们能与线粒体DNA竞争，从而导致生长受损。所有九种抑制质粒均含有小插入，对应于或包括线粒体tRNA（tRNATrp，tRNAGly或tRNAVal）或tRNA样序列。插入位于对应于主要质粒转录物的5'末端的位置或在主要5'RNA末端的序列的同源附近的下游24个核苷酸。抑制性质粒的结构表明，tRNA是通过RNA中间体插入的。野生型质粒转录物的3'端本身可以折叠成具有tRNA样特征的二级结构，类似于植物病毒RNA的3'端的tRNA样结构。该结构可以在通过逆转录的质粒复制中起作用。抑制性质粒的主要转录物始于插入的线粒体tRNA序列的5'端，其浓度比野生型质粒的转录物高25至100倍。插入的mtDNA序列中5'RNA末端的定位可识别一个短共有序列（PuNPuAG），该序列存在于线粒体tRNA基因子集的5'末端。该序列与紧邻质粒上游的序列一起形成更长的共有序列，该序列类似于神经孢菌线粒体DNA中转录起始位点的序列。质粒的抑制行为很可能与tRNA的插入直接相关，从而导致质粒转录本的过量产生。

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