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J. Biol. Chem., Vol. 268, Issue 18, 13748-13755, 06, 1993

A difference in the rate of ribosomal elongation balances the synthesis of eukaryotic translation initiation factor (eIF)-2 alpha and eIF-2 beta

JA Chiorini, TR Boal, S Miyamoto and B Safer
Section on RNA and Protein Biosynthesis, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.

Eukaryotic translation initiation factor 2 (eIF-2) is a heterotrimer composed of three subunits designated alpha, beta, and gamma. 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-2 beta was five times more abundant than eIF-2 alpha. However, immunoprecipitation of pulse-labeled K562 cells showed an equimolar rate of synthesis of eIF-2 alpha and -beta despite the 5-fold difference in the size of their mRNA pools. Addition of equal amounts of synthetic capped mRNA for eIF-2 alpha and eIF-2 beta to an in vitro translation reaction produced five times more eIF-2 alpha protein than eIF-2 beta. Determination of the polysome profile for alpha and beta mRNA in K562 cells indicated eIF-2 alpha was translated more efficiently than eIF-2 beta. Substitution of either the initiation codon context or the leader of the beta mRNA for that of alpha had only a minor effect on the translational efficiency of beta. Comparison of the rate of ribosomal elongation for the two mRNAs indicated that ribosomes associated with the beta mRNA elongate at a rate 4-fold less than that of eIF-2 alpha. Thus, the balanced translation of alpha and beta mRNA is primarily the result of a 4-fold difference in the rate of ribosomal elongation.
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This article has been cited by other articles:

				J. A. Chiorini, S. Miyamoto, S. J. Harkin, and B. Safer Genomic Cloning and Characterization of the Human Eukaryotic Initiation Factor-2beta Promoter J. Biol. Chem., February 12, 1999; 274(7): 4195 - 4201. [Abstract] [Full Text] [PDF]