Eukaryotic translation initiation factor 2 (eIF-2) is a heterotrimer composed of three subunits designated α, β, and γ. These proteins exist in equimolar amounts in the cell and have not been detected as isolated subunits. Our research examines the basis of their balanced synthesis. Northern analysis of K562 cell mRNA revealed that eIF-2β was five times more abundant than eIF-2α. However, immunoprecipitation of pulse-labeled K562 cells showed an equimolar rate of synthesis of eIF-2α and -β despite the 5-fold difference in the size of their mRNA pools. Addition of equal amounts of synthetic capped mRNA for eIF-2α and eIF-2β to an in vitro translation reaction produced five times more eIF-2α protein than eIF-2β. Determination of the polysome profile for α and β mRNA in K562 cells indicated eIF-2α was translated more efficiently than eIF-2β. Substitution of either the initiation codon context or the leader of the β mRNA for that of α had only a minor effect on the translational efficiency of β. Comparison of the rate of ribosomal elongation for the two mRNAs indicated that ribosomes associated with the β mRNA elongate at a rate 4-fold less than that of eIF-2α. Thus, the balanced translation of α and β mRNA is primarily the result of a 4-fold difference in the rate of ribosomal elongation.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - Jun 25 1993|
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