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 transla tion elongation factors 1 alpha (EF-1 alpha) and 2 (EF-2) from a mitoc hondrion-lacking protozoan, Glugea plecoglossi, that belongs to micros poridians were determined, The deduced amino acid sequences of the put ative EF-1 alpha and EF-2 of Gl. plecoglossi showed very unusual featu res compared with typical eukaryotic sequences, The degree of divergen ce was especially great in the EF-1 alpha sequence, although it clearl y showed a eukaryotic feature when aligned with homologs from the thre e primary kingdoms, Phylogenetic analyses of EF-1 alpha and EF-2 on th e basis of the maximum likelihood method of protein phylogeny clearly and consistently suggested that among eukaryotic species being analyze d, Gl. plecoglossi and another mitochondrion-lacking protozoan, Giardi a lamblia, respectively represent the earliest and the second earliest offshoots of eukaryotes, When the EF-1 alpha and EF-2 phylogenies wer e totally evaluated, the earliest divergence of Gl. plecoglossi in euk aryotes became more clearly confirmed. If the phylogenetic relationshi ps inferred from the present analysis are correct, microsporidians mig ht be extremely ancient eukaryotes that diverged before the occurrence of mitochondrial symbiosis.