Immunochemical Cross-Reactivities of Protein Synthesis Elongation Factors (EF-Tu and EF-1α Proteins) Support the Phylogenetic Coherence of Archaebacteria

Summary Elongation factor Tu (EF-Tu) proteins have been purified by affinity chromatography on GDP-Sepharose columns, from the eubacterium Thermotoga maritima and from archaebacteria (Sulfolobus solfataricus, Thermoproteus tenax, Thermococcus celer, Pyrococcus wosei, Archaeoglobus fulgidus, Methanococcus thermolitotrophicus, Thermoplasma acidophilum) representative of all known divisions in the arachaebacterial tree except halophiles. Polyclonal antibodies raised against the purified Tu proteins were challenged with homologous and heterologous factors including eukaryotic EF-1α and cross-reactivities were quantified using 125 I labelled Protein A as the reporter molecule. The immunochemical relationships among factors both within and across kingdom boundaries demonstrated that (i) every archaebacterial EF-Tu is closer (immunochemically) to every other archaebacterial EF-Tu than to the analogous proteins of eubacteria and eukaryotes, (ii) within the archaebacteria the immunochemical cross-reactivities grossly correlate with the phylogenetic relatedness of the organisms inferred from similarities in rRNA sequences. The data support the notion that archaebacteria form a phylogenetically coherent taxon.