Determination of the amounts of protein synthesis initiation factors required for translation of rabbit alpha-globin and beta-globin mRNAs.

alpha-Globin mRNA was translated at 60-80% of the rate of beta-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 (C0.5) of these mRNAs were determined in the partially purified system from wheat germ. The C0.5s of eIF-3, eIF-2 and eIF-4F were found to be about the same. The C0.5s of eIF-4C and eIF-4A for alpha-globin mRNA were only slightly higher (1.5-fold) than those of beta-globin mRNA. The C0.5 for eIF-4B was 2.5-fold higher for alpha-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 alpha-globin mRNA. These results indicate that the difference in the rate of translation of alpha- and beta-globin mRNAs is not due solely to the amounts of factors required.