Filée Jonathan, Forterre Patrick
Laboratoire de Microbiologie et Génétique Moléculaire, CNRS UMR-5100, 118 Route de Narbonne, 31062 Toulouse Cedex 04, France.
Trends Microbiol. 2005 Nov;13(11):510-3. doi: 10.1016/j.tim.2005.08.012. Epub 2005 Sep 12.
Although mitochondria derive from alpha-proteobacteria, many proteins acting in this organelle did not originate from bacteria. In particular, phylogenetic evidence indicates that RNA polymerase, DNA polymerase and DNA primase--with homologues encoded by T3/T7-like bacteriophages--have replaced the ancestral proteins of bacterial origin. To date, there was no clear explanation for this puzzling observation. Bacterial genomics has now revealed the presence of cryptic prophages that are related to T3/T7 in several genomes of proteobacteria. We propose that such a prophage was present in the ancestral alpha-proteobacterium at the origin of mitochondria and that RNA polymerase, DNA polymerase and DNA primase encoded by this prophage replaced the original bacterial enzymes to function in mitochondria. Another T3/T7 viral-like RNA polymerase is functional in the chloroplast, indicating that a strong selection pressure has favored replacement of some cellular proteins by viral proteins in organelle evolution.
尽管线粒体起源于α-变形菌，但在这个细胞器中起作用的许多蛋白质并非起源于细菌。特别是，系统发育证据表明，RNA聚合酶、DNA聚合酶和DNA引发酶（具有由T3/T7样噬菌体编码的同源物）已经取代了起源于细菌的祖先蛋白质。迄今为止，对于这一令人困惑的观察结果尚无明确解释。细菌基因组学现已揭示，在几种变形菌的基因组中存在与T3/T7相关的隐蔽原噬菌体。我们提出，在线粒体起源时，这种原噬菌体存在于祖先α-变形菌中，并且由该原噬菌体编码的RNA聚合酶、DNA聚合酶和DNA引发酶取代了原始的细菌酶，以便在线粒体中发挥作用。另一种T3/T7病毒样RNA聚合酶在叶绿体中起作用，这表明在细胞器进化过程中，强大的选择压力有利于用病毒蛋白取代一些细胞蛋白质。
