Conclusions

    Of all the genes functioning in translation that have been sequenced to date, the EF-Tu molecule seems to offer the most reliable indication of early divergences. Genome analyses show it is the slowest evolving sequence of its class and should, therefore, be the most reliable for phylogenetic purposes. It is also unlikely to be laterally transferred between organisms because it is present in all cells and, during protein synthesis, interacts with cellular components that are dispersed throughout the bacterial genome. Furthermore, direct phylogenetic analyses of this molecule by almost all authors support the eocyte tree. Significant support for the eocyte tree also comes from the observations that eukaryotic ribosomal operons are organized like those of Sulfolobus, Desulfurococcus, and Thermoproteus and not organized like the tRNA containing rRNA operons of halobacteria, methanogens, and eubacteria.