The Chaperonin Genes of Jakobid Protists

摘要具有最像真细菌的线粒体基因组的组织应该具有最原始的线粒体和真核蛋白质折叠机制。第一组(cpn60，线粒体，真细菌后代)和第二组(CCT，胞质，古细菌后代)伴侣蛋白基因的序列，与原核外群和其他原生生物(包括非线粒体样本)的序列进行比较，应该可以揭示这一点是否属实。此外，拥有最像真细菌的线粒体基因组的生物应该有祖先的内含子分布。大多数被认为是祖先的真核生物缺乏剪接体内含子，但越来越多的证据表明这些内含子已经丢失。与这一解释一致的是，初步数据显示，雅各布类中存在大量剪接体内含子。Jakobid鞭毛虫中的CPN 60和CCT亚基将被测序，目前培养中有8种线粒体。使用聚合酶链式反应技术进行的初步测序之后，将根据基因组自由进行更完整的测序。这些序列的进化史将通过系统发育分析来推断，这些分析纠正了稀疏分类单元采样的有害影响和诸如长分支吸引之类的人工制品。内含子的丰度和结构将根据目前关于真核细胞内含子进化的假设进行评估。Jakobid鞭毛虫可能是现存真核生物的祖先之一。Jakobid线粒体基因组在基因含量、基因组织和推测的基因功能方面代表了已发现的最像真细菌的线粒体基因组。此外，几乎所有的非线粒体原生动物都被证明保留了线粒体起源的基因，这表明它们来自线粒体祖先。Jakobid鞭毛虫可能是研究早期真核生物进化的一个信息模型系统。

AbstractOrganisms with the most eubacterial-like mitochondrial genomes should have the most ancestral mechanisms for mitochondrial and eukaryotic protein-folding machinery. Sequences of the group I (cpn60, mitochondrial, descended from eubacteria) and group II (CCT, cytosolic, descended from archaea) chaperonin genes, compared with those from prokaryotic outgroups and from other protists including amitochondriate exemplars, should reveal whether this is so. In addition, the organisms with the most eubacterial-like mitochondrial genomes should have an ancestral intron distribution. Most eukaruyotes that are considered to be ancestral lack spliceosomal introns, but evidence is accumulating that these introns were lost. Consistent with this interpretation, preliminary data show the presence of numerous spliceosomal introns in jakobids. Cpn 60 and CCT subunits in jakobid flagellates, of which there are currently eight mitochondriate species in culture, will be sequenced. Initial sequence surveys using PCR techniques will be followed by more complete sequencing based upon genomic liberties. The evolutionary histories of these sequences will be inferred through phylogenetic analyses that correct for the deleterious effects of sparse taxon sampling and such artifacts as long-branch attraction. The abundance and structure of included introns will be assessed in the light of current hypotheses about the evolution of introns in eukaryotic cells. The jakobid flagellates are potentially among the ancestral of living eukaryotes. Jakobid mitochondrial genomes represent the most eubacterial-like mitochondrial genomes discovered, in terms of gene content, gene organization, and putative gene function. Moreover, nearly all groups of amitochondrial protist have been shown to retain genes of mitochondrial origin, suggesting that they are derived from mitochondriate ancestors. The jakobid flagellates may represent an informative model system for the study of early eukaryote evolution.