Formal Proof that the Split Genes of tRNAs of Nanoarchaeum equitans Are an Ancestral Character
Formal Proof that the Split Genes of tRNAs of Nanoarchaeum equitans Are an Ancestral Character
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DOI：
10.1007/s00239-009-9280-z
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发表时间：
2009-11-01
影响因子：
3.9
通讯作者：
Di Giulio, Massimo
中科院分区：
文献类型：
--
作者：
Di Giulio, Massimo
证据表明，Nanoarchaeum equalans 的 tRNA 分子分裂为 50 和 30 半的基因是一种祖先特征。首先，将证明存在自然连续的进化阶段，按照当今已知的 tRNA 的三种基因结构的顺序形成：（i）tRNA 的分裂基因，（ii）具有内含子的 tRNA 基因，以及（iii）连续编码 tRNA 分子的 tRNA 基因。这一系列的进化阶段将 tRNA 的分裂基因识别为拟态特征。此外，通过证明所有可能的剩余五个进化阶段连续都是错误的来证明这一进化阶段连续是正确的。事实上，将分裂基因视为派生特征的进化阶段演替被证明是错误的，因为这种演替所固有的复杂性的增加不能通过tRNA的分裂基因来证明是合理的，因为这些不能赋予任何选择优势来证明这种复杂性的增加是合理的。此外，遗传漂变无法解释 tRNA 分裂基因的进化，因为在这些生物体中观察到的群体遗传有效规模巨大。进化阶段的其余四个连续也是错误的，因为：（i）它们不是进化阶段的自然连续，（ii）这些进化阶段的绝对观察频率足以明确排除它们可能是进化阶段的自然连续，并且（iii）其中两个是伪造的，因为它们没有将带有内含子的 tRNA 基因的进化阶段与 tRNA 分裂基因的进化阶段置于密切的进化关系中，相反，被证明具有密切的进化联系。因此，只剩下进化阶段的连续性，考虑到编码 50 和 30 半的 tRNA 的分裂基因，作为一种拟态特征，作为与本文提出的所有论点兼容的唯一连续性，并且作为在 tRNA 分子进化过程中实际运行的连续性。这个证明有两个非常重要的意义。一是关于 tRNA 分子是如何起源的；考虑到tRNA是如何起源于两个发夹样结构的结合，tRNA的分裂基因可能是该分子进化所经历的过渡阶段。另一个问题是tRNA的基因起源于何时，得出的结论是这些基因的起源是多系的，即不是单系的，因此与当前范式的假设相反。
A proof is given that the genes of the tRNA molecule of Nanoarchaeum equitans split into the 50 and 30 halves are an ancestral trait. First, the existence of a natural succession of evolutionary stages will be proven, formed in the order of the three gene structures of tRNAs known today: (i) the split genes of tRNAs, (ii) the genes of tRNAs with introns, and (iii) the genes of tRNAs continuously codifying for the tRNA molecule. This succession of evolutionary stages identifies the split genes of tRNAs as a pleisiomorphic character. The proof that this succession of evolutionary stages is, moreover, true is performed by proving that all the possible remaining five successions of evolutionary stages are false. Indeed, the succession of evolutionary stages considering split genes as a derived character turns out to be false in that the increase in complexity inherent to this succession cannot be justified by the split genes of tRNAs because these could not have conferred any selective advantage justifying this increase in complexity. Furthermore, genetic drift is unable to explain the evolution of split genes of tRNAs because of the enormous genetic effective size of the population observed in these organisms. The remaining four successions of evolutionary stages are also false because: (i) they are not natural successions of evolutionary stages, (ii) the absolute observed frequencies of these evolutionary stages are such as to exclude categorically that they might be natural successions of evolutionary stages, and also (iii) two of these are falsified by the fact that they do not place the evolutionary stage of genes of tRNAs with introns in a close evolutionary relationship with that of the split genes of tRNAs which can, instead, be proven to have a close evolutionary link. Therefore, there remains only the succession of evolutionary stages considering the split genes of tRNAs codifying for the 50 and 30 halves, as a pleisiomorphic character, as the only succession compatible with all the arguments presented in this article and as the one that actually operated during the evolution of the tRNA molecule. This proof has two very important implications. One regards how the tRNA molecule originated; considering how tRNA originated as the union of two hairpin-like structures, the split genes of tRNAs might be the transition stage through which the evolution of this molecule passed. The other regards when the genes of tRNAs originated, reaching the conclusion that the origin of these genes is polyphyletic, i.e. not monophyletic and hence contrary to the assumptions of the current paradigm.