Distinct epitopes in eukaryotic initiation factor 2 for binding of mRNA and for ternary complex formation with...

Eukaryotic initiation factor 2 (eIF-2) forms a ternary complex with methionyl-tRNA(fMet) and GTP on one hand, and it binds to a specific site in mRNA molecules on the other. Antibodies directed against eIF-2 were used to analyze these dual binding activities. A monoclonal antibody directed against the beta-subunit of eIF-2, 5A4, is able to inhibit ternary complex formation as well as binding of mRNA, showing that this subunit is essential for both binding activities of eIF-2. However, a polyclonal antibody, PR1, is able to distinguish between these activities in the eIF-2 molecule. In the presence of PR1, binding of mRNA by eIF-2 is inhibited completely, yet ternary complex formation with methionyl-tRNA(fMet) and GTP is stimulated more than 5-fold. Apparently, specific antibodies to eIF-2 can induce a conformational change in inactive factor molecules that permits them to form ternary complexes. These results show that distinct epitopes in eIF-2 are involved in binding of mRNA and in ternary complex formation with methionyl-tRNA(fMet) and GTP.