Determination of the Amounts of Protein-Synthesis Initiation-Factors Required for Translation of Rabbit α-Globin and β-Globin mRNAs

α-Globin mRNA was translated at 60-80% of the rate of β-globin mRNA in a rabbit reticulocyte lysate, a wheat germ S30 and in a wheat germ partially purified system. The concentrations of the initiation factors (eIF-) required to obtain half-maximal rate of translation (C 0.5) of these mRNAs were determined in the partially purified system from wheat germ. The C 0.5s of eIF-3, eIF-2 and eIF-4F were found to be about the same. The C 0.5s of eIF-4C and eIF-4A for α-globin mRNA were only slightly higher (1.5-fold) than those of β-globin mRNA. The C 0.5 for eIF-4B was 2.5-fold higher for α-globin mRNA. Addition of saturating amounts of these initiation factors to either the S-30 system or the partially purified system did not increase the rate of translation of α-globin mRNA. These results indicate that the difference in the rate of translation of α and β-globin mRNAs is not due solely to the amounts of factors required.