Complete nucleotide sequences of the genes encoding translation elongation factors 1 alpha and 2 from a microsporidian parasite, Glugea plecoglossi: implications for the deepest branching of eukaryotes.

Complete nucleotide sequences of the genes putatively encoding translation elongation factors 1 alpha (EF-1 alpha) and 2 (EF-2) from a mitochondrion-lacking protozoan, Glugea plecoglossi, that belongs to microsporidians were determined. The deduced amino acid sequences of the putative EF-1 alpha and EF-2 of Gl. plecoglossi showed very unusual features compared with typical eukaryotic sequences. The degree of divergence was especially great in the EF-1 alpha sequence, although it clearly showed a eukaryotic feature when aligned with homologs from the three primary kingdoms. Phylogenetic analyses of EF-1 alpha and EF-2 on the basis of the maximum likelihood method of protein phylogeny clearly and consistently suggested that among eukaryotic species being analyzed, Gl. plecoglossi and another mitochondrion-lacking protozoan, Giardia lamblia, respectively represent the earliest and the second earliest offshoots of eukaryotes. When the EF-1 alpha and EF-2 phylogenies were totally evaluated, the earliest divergence of Gl. plecoglossi in eukaryotes became more clearly confirmed. If the phylogenetic relationship inferred from the present analysis are correct, microsporidians might be extremely ancient eukaryotes that diverged before the occurrence of mitochondrial symbiosis.