Hypusine‐containing Protein eIF5A Promotes Translation Elongation

Abstract

The factor eIF5A, the sole protein in eukaryotes and archaea containing the unusual amino acid hypusine [Nε‐(4‐amino‐2‐hydroxybutyl)lysine], was originally identified based on its ability to stimulate the yield (endpoint) of methionyl‐puromycin synthesis, a model assay for first peptide bond synthesis thought to report on certain aspects of translation initiation. In Saccharomyces cerevisiae, eIF5A is encoded by the genes TIF51A and TIF51B; and both in yeast cells and in model assays of eIF5A function, hypusine formation is essential for eIF5A activity. Using molecular genetic and biochemical assays, we found that eIF5A promotes translation elongation. Depletion or inactivation of eIF5A in yeast impaired protein synthesis and resulted in the accumulation of polysomes and an increase in ribosomal transit times. Addition of recombinant eIF5A from yeast, but not a derivative lacking hypusine, restored translational activity in extracts prepared from eIF5A mutant strains and enhanced the rate of tripeptide synthesis in reconstituted translation assays. Moreover, inactivation of eIF5A mimicked the effects of the eEF2 inhibitor sordarin, indicating that eIF5A might function late in the translation elongation cycle like eEF2. As eIF5A is a structural homolog of the bacterial protein EF‐P, we propose that eIF5A/EF‐P is a universally conserved translation elongation factor.