CONSERVATION OF THE AMINO-TERMINAL EPITOPE OF ELONGATION-FACTOR TU INEUBACTERIA AND ARCHAEA

An epitope of elongation factor Tu (EF-Tu), which is found in organism s in both the bacterial and archaeal domains, was recently defined by mAb 900. To localize the conserved epitope within the EF-Tu molecule a nd to determine its sequence, SPOTScan analysis of synthetic peptides, Western blot analysis of purified EF-Tu domains and site-directed mut agenesis studies were used. Analysis of mAb 900 binding to overlapping 15-mer peptides encompassing the complete sequence of EF-Tu of Escher ichia coli was inconclusive, suggesting three distinct regions may be epitopes. Western blot analysis of EF-Tu domains 1-3 of Thermus thermo philus suggested that the epitope was located at the N terminus. This was confirmed by site-directed mutagenesis of EF-Tu domain 1 of Mycopl asma hominis. By C-terminal truncation of the N-terminal 15-mer peptid e the epitope was mapped to EF-Tu residues 1-6. Replacement of each of the residues in the epitope peptide demonstrated that only positions 5 and 6 were indispensable for antibody binding. These data provide ev idence that the highly conserved epitope recognized by mAb 900 in the bacterial and archaeal domains is located at the very end of the N ter minus of the EF-Tu molecule.