Regulation of protein synthesis in eukaryotes: Mode of action of eRF, an eIF‐2‐recycling factor from rabbit reticulocytes involved in GDP/GTP exchange

Abstract

The rate of initiation of protein synthesis appears to be controlled at the level of recycling of eIF‐2. In this process a new factor, designated eRF, plays an important role. The factor has been purified from the postribosomal supernatant and has been called formerly anti‐HRI and anti‐inhibitor [Amesz, H., Goumans, H., Haubrich‐Morree, Th., Voorma, H. O., and Benne, R. (1979) Eur. J. Biochem. 98, 513–520]. Its effect on the initiation of protein synthesis has been studied in several assays: a small but distinct effect is found in the assay for the formation of a ternary complex between eIF‐2, GTP and Met‐tRNA; a 4–5‐fold stimulation is obtained in assays for 40S preinitiation complex formation and in the methionyl‐puromycin reaction. In the latter assay a catalytic use of eIF‐2 occurs provided that eRF is present. eRF forms a complex with eIF‐2 which results in a decrease of the affinity of eIF‐2 for GDP, giving it the properties of a GDP/GTP exchange factor. The model stresses the catalytic use of eIF‐2 in initiation provided that conditions are met for GDP/GTP exchange by a transient complex formation between eIF‐2 and eRF. On the other hand, it is shown that phosphorylation of eIF‐2 by the hemin‐regulated inhibitor (HRI) abolishes the recycling of eIF‐2, by the formation of another stable complex comprising eIF‐2αP, GDP and eRF. Copyright © 1984, Wiley Blackwell. All rights reserved