Phylogenetic Position of Amitochondriate Protists in the Evolution of Eukaryotes.

Mitochondria are very likely to have descended from eubacteria by endosymbiosis. Therefore, phylogenetic placement of amitochondriate protists is important in understanding the origin and early evolution of eukaryotes. That is, if some of the amitochondriate protists turn out to represent deep branchings in the eukaryotic tree, they are very likely to be living relics of the earliest phase of eukaryotic evolution-before the endosymbiotic origin of proto-mitochondria. We have investigated the phylogenetic relationship among protists, including amitochondrial ones, by analyzing amino acid sequences of translation elongation factors (EF-lalpha and EF-2) and isoleucyl- and valyltRNA synthetases (ileRS and valRS). Until now, both of the EF phylogenies (EF-lalpha tree is