Early evolution of eukaryotes inferred from protein phylogenies of translation elongation factors 1α and 2

On the basis of the maximum likelihood (ML) method of protein phylogenetics, we have examined a protozoan phylogeny by using the amino acid sequences of translation elongation factors EF-1α and EF-2. When the results of individual ML analysis were totally evaluated, it was suggested (a) that three mitochondrion-lacking lineages, microsporidians, diplomonads, and trichomonads have diverged from the line leading to higher eukaryotes in the early phase of eukaryotic evolution, (b) that microsporidians are the earliest offshoot of eukaryotes among these three lineages, and (c) that Euglenozoa are not likely to have diverged next to diplomonads as suggested by the small subunit ribosomal RNA (SrRNA) tree, but show a close affinity with higher eukaryotes. Previous results have shown that the amino acid compositions of EF-1α and EF-2 do not differ significantly among species, and hence the present EF phylogenies are expected to give a robust estimation for early divergences of eukaryotes.