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

Publisher Website
Google Scholar
Abstract
The rate of initiation of protein synthesis appears to be controlled at the level of recycling of eIF-2 [eukaryotic initiation factor 2]. In this process a new factor, designated eRF, plays an important role. The factor was purified from the post-ribosomal supernatant and was called formerly anti-HRI [hemin-regulated inhibitor] and anti-inhibitor. Its effect on the initiation of protein synthesis was studied in several asays: 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- to 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, phosphorylation of eIF-2 by HRI abolishes the recycling of eIF-2, by the formation of another stable complex comprising eIF-2.alpha.P, GDP and eRF.