Kennell J C, Saville B J, Mohr S, Kuiper M T, Sabourin J R, Collins R A, Lambowitz A M
Department of Molecular Genetics, Ohio State University, Columbus 43210-1292.
Genes Dev. 1995 Feb 1;9(3):294-303. doi: 10.1101/gad.9.3.294.
The mitochondria of certain natural isolates of Neurospora contain both the Varkud plasmid, which encodes a reverse transcriptase, and a small unrelated RNA (VS RNA) that performs RNA-mediated self-cleavage and ligation reactions. Here, we show that VS RNA is transcribed from a VS plasmid DNA template by the Neurospora mitochondrial RNA polymerase using a promoter located immediately upstream of the RNA self-cleavage site that generates monomeric transcripts. VS RNA is then reverse transcribed by the Varkud plasmid reverse transcriptase to yield a full-length (-) strand cDNA, a predicted replication intermediate. Combined with previous genetic evidence, our results indicate that the VS plasmid replicates by reverse transcription as a satellite of the Varkud plasmid. This mode of replication, unprecedented for a satellite RNA, likely reflects the promiscuity of the Varkud plasmid reverse transcriptase, which does not require a specific primer to initiate cDNA synthesis. Our findings indicate how primitive reverse transcriptases with similar relaxed specificity could have facilitated the evolution of new retroelements.
某些粗糙脉孢菌自然分离株的线粒体中既含有编码逆转录酶的瓦尔库德质粒，也含有一种小型非相关RNA（VS RNA），该RNA能进行RNA介导的自我切割和连接反应。在此，我们表明VS RNA是由粗糙脉孢菌线粒体RNA聚合酶以位于产生单体转录本的RNA自我切割位点上游紧邻处的启动子，从VS质粒DNA模板转录而来。然后，VS RNA被瓦尔库德质粒逆转录酶逆转录，产生一条全长（-）链cDNA，这是一种预测的复制中间体。结合先前的遗传学证据，我们的结果表明VS质粒作为瓦尔库德质粒的卫星通过逆转录进行复制。这种复制模式对于卫星RNA来说是前所未有的，可能反映了瓦尔库德质粒逆转录酶的混杂性，该酶启动cDNA合成不需要特定引物。我们的发现揭示了具有类似宽松特异性的原始逆转录酶如何促进新反转录元件的进化。
