Role of Translation Factor eIF5A and its Hypusine Modification in Synthesis of Polyproline Proteins
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In addition to the small and large ribosomal subunits, aminoacyl-tRNAs, and mRNA, cellular protein synthesis is dependent on translation factors. Since its discovery nearly 40 years ago, eIF5A is one such factor that has remained a mystery. eIF5A was initially characterized based on its ability to stimulate methionyl-puromycin synthesis, a model assay for protein synthesis; however, the function of this factor in cellular protein synthesis has been difficult to resolve. Interestingly, eIF5A is the sole cellular protein to contain the post-translational hypusine modification. Hypusine formation requires the conserved enzymes deoxyhypusine synthase and deoxyhypusine hydroxylase for its biosynthesis. This dissertation focuses on the novel role of the translation factor eIF5A and its hypusine modification in the elongation phase of protein synthesis. Combining yeast genetic and biochemical techniques, we uncover new functional and mechanistic insights for the role of eIF5A and its hypusine modification in translation. Similar to its bacterial homolog EF-P, eIF5A stimulates the production of proteins containing runs of consecutive proline residues. In addition, genome-wide ribosome profiling studies reveal ribosomal pausing and drop-off on mRNA sequences encoding polyproline. Moreover, molecular analyses of eIF5A mutants dependent on the conserved hydroxyl group on hypusine demonstrate that the second step of hypusine synthesis contributes to the translation function of the factor. Taken together, these discoveries delineate the extraordinary role of eIF5A and its hypusine modification in the synthesis of polyproline sequences and reinforces the position of eIF5A as a crucial factor in translation elongation.