Eukaryotic translation initiation factor 2 (eIF-2) is a heterotrimer of three subunits designated alpha, beta, and gamma. Since they are found in equimolar amounts in the cell and are never detected as isolated subunits, we examined the basis of their balanced synthesis. Northern analysis of the K562 mRNA revealed the message for beta was five times more abundant than the message for alpha. Further analysis of total RNA from other human tissues showed that this difference in the pool sizes for the two messages was present in a variety of tissues. However, the magnitude of the difference varied between the tissues. The difference in pool sizes ranged from 3.6:1 in heart and brain to 15:1 in pancreas. Immunoprecipita-tion of eIF-2 alpha and beta protein from K562 cells labeled for times as short as 10 min revealed equimolar synthesis of alpha and beta despite a five-fold difference in the size of the mRNA pools. Comparison of the polysome profile for alpha and beta in K562 cells showed that the average alpha message had over 50% more ribosomes associated with it than the average beta message. Finally, addition of equal amounts of synthetic capped message for eIF-2 alpha and beta to micrococcal nuclease treated rabbit reticulocyte lysate resulted in 5 times more alpha protein being produced than beta. Thus the balanced translation of alpha and beta observed in vivo could be duplicated in vitro. We are currently investigating the mechanism which allows alpha to be translated more efficiently than beta and the biological significance of this balanced expression. In addition since only a partial cDNA sequence is available for beta, we have undertaken the isolation of a genomic clone for beta.
