Characterization of the interaction of eukaryotic initiation factors eIF-2 with eIF-2B

Modulation of protein/protein interaction is an important mechanism involved in the regulation of protein synthesis initiation. In particular, regulation of the interaction of eIF-2 with the guanine nucleotide exchange factor, eIF-2B, is involved in controlling protein synthesis under a variety of conditions. Phosphorylation of the a-subunit of eIF-2 converts the protein into a competitive inhibitor of eIF-2B by causing an increase in the affinity of the two proteins for each other. Consequently, it has been assumed that the a-subunit of eIF-2 is directly involved in the binding reaction. In the present study, the interaction of the two factors purified from rat liver was examined by Far Western analysis and by ELISA techniques. On Far Western blots, eIF-2B binds to the β, not the a, subunit of eIF-2. In addition, eIF-2 binds to the δ- and ε-subunits of elF-2B as well as to the recombinant eIF-2Bδ protein. In confirmation of earlier studies, phosphorylation of eIF-2a by HCR caused an increase in the affinity of the factor for eIF-2B. Unexpectedly, phosphorylation of the -subunit of eIF-2 by casein kinase II also increased the affinity of eIF-2B for eIF-2. In contrast, phosphorylation of either eIF-2α or eIF-2β had no effect on the interaction of eIF-2 with isolated recombinant elF-2Bδ. Finally, deletion mutants are currently being constructed to more precisely define the binding site of eIF-2Rδ for eIF-2 as well as the binding site on eIF-2β for eIF-2B.