Eukaryotic Translation Initiation Factor 5A (EIF5A)

The eukaryotic initiation factor 5A is an 18-kD protein composed of 154 amino acids. It contains a unique amino acid residue, hypusine, that is formed posttranslationally via the transfer and hydroxylation of the butylamino-group from the polyamine spermidine to a lys50 within the EIF5A protein. Depletion or inactivation of EIF5A in the yeast S. cerevisiae 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, enhanced the rate of tripeptide synthesis in vitro. Moreover, inactivation of EIF5A mimicked the effects of the EEF2 inhibitor sordarin, indicating that EIF5A might function together with EEF2 to promote ribosomal translocation.