Wheat germ eIF2 and CoeIF2. Resolution and functional characterization in in vitro protein synthesis

A factor that binds Met-tRNAiMet in a ternary complex (eucaryotic initiation factor (eIF2) ) and an auxiliary component that strongly stimulates the activity of the binding factor (CoeIF2) have been purified from extracts of wheat germ. The molecular weights of the two factors, as determined by glycerol gradient centrifugation and sodium dodecyl sulfate gel electrophoresis, are 88,000 and 20,000, respectively. Incubation of wheat germ eIF2 with gamma-[32P]ATP and alpha-subunit kinase results in the phosphorylation of a Mr = 40,500 subunit, while no specific phosphorylations are found when the eIF2 is incubated with the beta-kinase. These data are interpreted to suggest that CoeIF2 is a monomer of Mr = 20,000 while eIF2 may be a dimer, containing subunits of Mr = 40,000 and 50,000. Both eIF2 and CoeIF2 are strongly required for in vitro amino acid polymerization, providing the first direct demonstration of the function of CoeIF2 in protein synthesis.