Gupta R S
Department of Biochemistry McMaster University Hamilton, Ontario, Canada.
Antonie Van Leeuwenhoek. 1997 Jul;72(1):49-61. doi: 10.1023/a:1000278224701.
The evolutionary relationships within prokaryotes and between prokaryotes and eukaryotes is examined based on protein sequence data. Phylogenies and common signature sequences in some of the most conserved proteins point to a close evolutionary relationship between Archaebacteria and Gram-positive bacteria. The monophyletic nature and distinctness of the Archaebacterial domain is not supported by many of the phylogenies. Within Gram-negative bacteria, cyanobacteria are indicated as the deepest branching lineage, and a clade consisting of Archaebacteria, Gram-positive bacteria and cyanobacteria is supported by signature sequences in many proteins. However, the division within the prokaryotic species, viz. Archaebacteria<-->Gram-positive bacteria-->Cyanobacteria-->other groups of Gram-negative bacteria, is indicated to be not very rigid but, instead is an evolutionary continuum. It is expected that certain species will be found which represent intermediates in the above transitions. By contrast to the evolutionary relationships within prokaryotes, the eukaryotic species, which are structurally very different, appear to have originated by a very different mechanism. Protein phylogenies and signature sequences provide evidence that the eukaryotic nuclear genome is a chimera which has received major contributions from both an Archaebacterium and a Gram-negative bacterium. To explain these observations, it is suggested that the ancestral eukaryotic cell arose by a symbiotic fusion event between the above parents and that this fusion event led to the origin of both nucleus and endoplasmic reticulum. The monophyletic nature of all extant eukaryotic species further suggests that a 'successful primary fusion' between the prokaryotic species that gave rise to the ancestral eukaryotic cell took place only once in the history of this planet.
基于蛋白质序列数据，研究了原核生物内部以及原核生物与真核生物之间的进化关系。一些最保守蛋白质中的系统发育和共同特征序列表明古细菌与革兰氏阳性菌之间存在密切的进化关系。许多系统发育研究并不支持古细菌域的单系性质和独特性。在革兰氏阴性菌中，蓝细菌被认为是分支最深的谱系，许多蛋白质中的特征序列支持由古细菌、革兰氏阳性菌和蓝细菌组成的一个进化枝。然而，原核生物物种内部的划分，即古细菌<-->革兰氏阳性菌-->蓝细菌-->其他革兰氏阴性菌群，并非非常严格，而是一个进化连续体。预计会发现某些代表上述过渡阶段中间状态的物种。与原核生物内部的进化关系形成对比的是，结构上差异很大的真核生物物种似乎起源于一种非常不同的机制。蛋白质系统发育和特征序列提供了证据，表明真核生物的核基因组是一种嵌合体，它从一种古细菌和一种革兰氏阴性菌都获得了主要贡献。为了解释这些观察结果，有人提出，祖先真核细胞是由上述亲本之间的共生融合事件产生的，并且这种融合事件导致了细胞核和内质网的起源。所有现存真核生物物种的单系性质进一步表明，导致祖先真核细胞的原核生物物种之间的“成功的初次融合”在这个星球的历史上只发生过一次。
