elF5A Promotes Translation of Polyproline Motifs

Translation factor elF5A, containing the unique amino acid hypusine, was originally shown to stimulate Met-puromycin synthesis, a model assay for peptide bond formation. More recently, elF5A was shown to promote translation elongation; however, its precise requirement in protein synthesis remains elusive. We use in vivo assays in yeast and in vitro reconstituted translation assays to reveal a specific requirement for elF5A to promote peptide bond formation between consecutive Pro residues. Addition of elF5A relieves ribosomal stalling during translation of three consecutive Pro residues in vitro, and loss of elF5A function impairs translation of polyproline-containing proteins in vivo. Hydroxyl radical probing experiments localized elF5A near the E site of the ribosome with its hypusine residue adjacent to the acceptor stem of the P site tRNA. Thus, elF5A, like its bacterial ortholog EFP, is proposed to stimulate the peptidyl transferase activity of the ribosome and facilitate the reactivity of poor substrates like Pro.