NUCLEOTIDE-SEQUENCE OF THE VARKUD MITOCHONDRIAL PLASMID OF NEUROSPORA AND SYNTHESIS OF A HYBRID TRANSCRIPT WITH A 5' LEADER DERIVED FROM MITOCHONDRIAL RNA
NUCLEOTIDE-SEQUENCE OF THE VARKUD MITOCHONDRIAL PLASMID OF NEUROSPORA AND SYNTHESIS OF A HYBRID TRANSCRIPT WITH A 5' LEADER DERIVED FROM MITOCHONDRIAL RNA
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DOI：
10.1016/0022-2836(88)90594-3
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发表时间：
1988-11-05
影响因子：
5.6
通讯作者：
LAMBOWITZ, AM
中科院分区：
文献类型：
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作者：
AKINS, RA;GRANT, DM;LAMBOWITZ, AM
脉孢菌的 Mauriceville 和 Varkud 线粒体质粒是密切相关的闭合环状 DNA（分别为 3.6 和 3.7 kb；1 kb = 103 个碱基或碱基对），其特征表明与线粒体 DNA 内含子和逆转录转座子的关系。在这里，我们对 Varkud 质粒的结构进行了表征，确定了其完整的核苷酸序列并绘制了其主要转录物图谱。 Mauriceville 和 Varkud 质粒具有超过 97% 的位置同一性。两种质粒均含有 710 个氨基酸的开放阅读框，编码逆转录酶样蛋白。该开放阅读框的氨基酸序列在两个质粒（701/710 个氨基酸）之间高度保守，正如功能上重要的蛋白质所预期的那样。两种质粒都有一个 0.4 kb 的区域，其中包含 5 个 PstI 回文结构和约 160 个碱基对的同向重复序列。该区域的序列比较表明，Varkud 质粒与共同祖先的差异小于 Mauriceville 质粒。通过 Northern 杂交实验检测到 Varkud 质粒的两个主要转录本：3.7 kb 的全长线性 RNA 和一个 4.9 kb 的额外突出转录本，比单体质粒长 1.2 kb。值得注意的是，我们发现 4-9 kb 转录物是一种杂合 RNA，由全长 3.7 kb Varkud 质粒转录物加上源自线粒体小 rRNA 5'' 端的 1.2 kb 5'' 前导序列组成。这一发现和其他发现表明，Varkud 质粒与某些 RNA 病毒一样，具有将异源 RNA 连接到其主要转录物 5'' 末端的机制，并且在某些情况下，线粒体中的核苷酸序列可能在 RNA 水平上重组。
The Mauriceville and Varkud mitochondrial plasmids of Neurospora are closely related, closed circular DNAs (3.6 and 3.7 kb, respectively; 1 kb = 103 bases or base-pairs), whose characteristics suggest relationships to mitochondrial DNA introns and retrotransposons. Here, were characterized the structure of the Varkud plasmid, determined its complete nucleotide sequence and mapped its major transcripts. The Mauriceville and Varkud plasmids have more than 97% positional identity. Both plasmids contain a 710 amino acid open reading frame that encodes a reverse transcriptase-like protein. The amino acid sequence of this open reading frame is strongly conserved between the two plasmids (701/710 amino acids) as expected for a functionally important protein. Both plasmids have a 0.4 kb region that contains five PstI palindromes and a direct repeat of approximately 160 base-pairs. Comparison of sequences in this region suggests that the Varkud plasmid had diverged less from a common ancestor than has the Mauriceville plasmid. Two major transcripts of the Varkud plasmid were detected by Northern hybridization experiments: a full-length linear RNA of 3.7 kb and an additional prominent transcript of 4.9 kb, 1.2 kb longer than monomer plasmid. Remarkably, we find that the 4-9 kb transcript is a hybrid RNA consisting of the full-length 3.7 kb Varkud plasmid transcript plus a 5'' leader of 1.2 kb that is derived from 5'' end of the mitochondrial small rRNA. This and other findings suggest that the Varkud plasmid, like certain RNA viruses, has a mechanism for joining heterologous RNAs to the 5'' end of its major transcript, and that, under some circumstances, nucleotide sequences in mitochondria may be recombined at the RNA level.