Characterization of initiation factor eIF-3 from wheat germ.

Initiation factor eIF-3 has been isolated from the 120 mM KCl postribosomal supernatant of wheat germ by chromatography on DEAE-cellulose and phosphocellulose. Glycerol gradient centrifugation and polyacrylamide gel electrophoresis under nondenaturing conditions indicate that the eIF-3 prepared in this manner is at least 85% pure. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate shows that the wheat germ eIF-3 contains 11 polypeptides, ranging in molecular weight from about 25,000 to 120,000. Eight of the polypeptides are present in equimolar amounts; two of the polypeptides are present at molar ratios of about 0.5; and one is present at a molar ratio of about 0.3. The highly purified wheat germ eIF-3 does not prevent the association of wheat germ 40S and 60 S ribosomal subunits to a significant extent. Wheat germ eIF-3 does not increase appreciably the ability of eIF-2 to form a ternary complex with Met-tRNAf and GTP. It does, however, enhance the binding of Met-tRNAf to 40 S ribosomal subunits in the presence of eIF-2 and GTP.