The Chaperonin Genes of Jakobid Protists

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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.