Protein synthesis in rabbit reticulocytes. Co-eIF-2A reverses mRNA inhibition of ternary complex (Met-tRNAf.eIF-2.GTP) formation by eIF-2.

mRNAs, at low concentrations, drastically inhibit ternary complex formation by eIF-2 (Met-tRNAf.eIF-2.GTP) and, when added to the preformed ternary complex, cause extensive dissociation of the complex. Co-eIF-2A stimulates (2- to 4-fold) Met-tRNAf binding to eIF-2 and, in the presence of excess Co-eIF-2A, the stimulated Met-tRNAf binding to eIF-2 is fully resistant to mRNAs. Other cofactors tested such as Co-eIF-2B and Co-eIF-2C do not reverse mRNA inhibition of ternary complex formation.