INITIATION-FACTOR EIF-4E OF SACCHAROMYCES-CEREVISIAE - DISTRIBUTION WITHIN THE CELL, BINDING TO MESSENGER-RNA, AND CONSEQUENCES OF ITS OVERPRODUCTION

The eukaryotic translational initiation factor 4E (eIF-4E) is an essen tial 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 c erevisiae was found to be similar to that observed in higher cells, wh ereby the yeast factor was more concentrated in the nucleus than in th e cytoplasm. Overexpression of yeast eIF-4E in S. cerevisiae exerted a t most a minimal effect on growth in liquid minimal medium and was not found to influence the translation of reporter gene mRNAs bearing sec ondary structure in their leader regions. In a new method to study mRN A-protein interactions, biotinylated mRNAs were synthesized in vitro f or use in studies of the binding of eIF-4E in yeast extracts. Streptav idin was used to adsorb the biotinylated mRNAs plus bound initiation f actors. Stem-loop structures in the leader region did not influence th e binding of eIF-4E or, in comparative experiments, of eIF-4A Thus yea st eIF-4E shows both similarities and differences with respect to the distribution and function of its counterparts in higher eukaryotes.