Initiation factor eIF-4E of Saccharomyces cerevisiae. Distribution within the cell, binding to mRNA, and consequences of its overproduction

Abstract

The eukaryotic translational initiation factor 4E (eIF-4E) is an essential protein that binds the 5' cap structure with high specificity and affinity. Yeast eIF-4E is homologous to eIF-4E of higher eukaryotes, but interacts with a different set of cap-binding complex proteins. In the present study the distribution of yeast eIF-4E in Saccharomyces cerevisiae was found to be similar to that observed in higher cells, whereby the yeast factor was more concentrated in the nucleus than in the cytoplasm. Overexpression of yeast eIF-4E in S. cerevisiae exerted at most a minimal effect on growth in liquid minimal medium and was not found to influence the translation of reporter gene mRNAs bearing secondary structure in their leader regions. In a new method to study mRNA-protein interactions, biotinylated mRNAs were synthesized in vitro for use in studies of the binding of eIF-4E in yeast extracts. Streptavidin was used to adsorb the biotinylated mRNAs plus bound initiation factors. Stem-loop structures in the leader region did not influence the binding of eIF-4E or, in comparative experiments, of eIF-4A. Thus yeast eIF-4E shows both similarities and differences with respect to the distribution and function of its counterparts in higher eukaryotes.