The Mechanism of Action of Eukaryotic Initiation Factor 4C in Protein Synthesis

Abstract

Binding of eukaryotic initiation factor 4C (eIF‐4C) to a 40‐S initiation complex could be detected by analysis of assay mixtures for 40‐S initiation complex formation on columns of Sepharose 6B and on sucrose gradients. On Sepharose 6B columns an almost stoichiometric binding of [14C]eIF‐4C was observed, provided that elF‐1, elF‐2, eIF‐3, Met‐tRNAf and mRNA were included in the assay mixtures. On sucrose gradients the presence of 0.5 μM edeine was an additional prerequisite for stable binding of eIF‐4C. The presence of eIF‐4C on the 40‐S initiation complex resulted in a pronounced increase of its stability, which might explain the observed stimulatory effect of the factor on the binding of Met‐tRNAf into initiation complexes. The interaction between eIF‐4C and the small ribosomal subunit presumably occurs at an early stage of the initiation process, since eIF‐4C was capable of dissociating 80‐S ribosomes into subunits. Protein synthesis in a ‘pH‐5’ assay was almost totally dependent on the addition of eIF‐4C, when the assay was performed with purified, nearly homogeneous, initiation factors. Copyright © 1980, Wiley Blackwell. All rights reserved