Mutation accumulation in transfer RNAs: Molecular evidence for Muller's ratchet in mitochondrial genomes
Mutation accumulation in transfer RNAs: Molecular evidence for Muller's ratchet in mitochondrial genomes
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DOI：
10.1093/oxfordjournals.molbev.a025557
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发表时间：
1996-01-01
影响因子：
10.7
通讯作者：
Lynch, M
中科院分区：
文献类型：
--
作者：
Lynch, M
有害突变的积累被认为是阻止相对于其有性祖先的专性无性血统长期存在的主要因素。这一现象与含有无性繁殖细胞器基因组的有性物种也有潜在的相关性。对动物线粒体和核基因组中转移RNA基因的比较研究表明，前者积累核苷酸替换的速度比后者快得多，而且有几条证据与过量替换有轻微危害的观点一致。首先，线粒体tRNAs茎中互补链之间的平均结合稳定性不到核tRNAs的一半。其次，随着进化时间的推移，线粒体tRNAs中的大多数环大小都经历了净减少，而且线粒体中的环大小比核基因组中的变化大近50倍。第三，尽管核tRNA基因中近20%的核苷酸(特别是那些参与三级相互作用的核苷酸)在所有动物类群和所有tRNA物种中是不变的，但在线粒体tRNA中没有不变的位点。这些观察结果以及最近的实验室实验结果，与以下假设一致：由于轻微有害突变的累积机会固定，未重组的细胞器基因组容易逐渐丧失适合性。
The accumulation of deleterious mutations is thought to be a major factor preventing the long-term persistence of obligately asexual lineages relative to their sexual ancestors. This phenomenon is also of potential relevance to sexual species that harbor asexually propagating organelle genomes. A comparative study of the transfer RNA genes in animal mitochondrial and nuclear genomes demonstrates that the former accumulate nucleotide substitutions much more rapidly than do the latter, and several lines of evidence are consistent with the idea that the excess substitutions are mildly deleterious. First, the average binding stability between complementary strands in the stems of mitochondrial tRNAs is less than half that in nuclear tRNAs. Second, most loop sizes in the mitochondrial tRNAs have experienced a net reduction in size over evolutionary time, and they are nearly 50 times more variable in the mitochondrial than in the nuclear genome. Third, although nearly 20% of the nucleotides in nuclear tRNA genes (particularly those involved in tertiary interactions) are invariant across all animal taxa and all tRNA species, there are no invariant sites in the mitochondrial tRNAs. These observations, as well as results from recent laboratory experiments, are consistent with the hypothesis that nonrecombining organelle genomes are subject to gradual loss of fitness due to the cumulative chance fixation of mildly deleterious mutations.