eIF5A is an indispensable protein for eukaryotic cells

Abstract

eIF5A is an evolutionarily conserved protein found in all eukaryotes, and in Archaea and bacteria. It functions as a translation factor promoting ribosomal elongation, and it can also bind to genes in the nucleus and to mRNA. eIF5A is encoded by two paralogous genes in most eukaryotes, with one copy (TIF51A in yeast and EIF5A1 in humans) highly expressed and essential, and the other (TIF51B in yeast and EIF5A2 in humans) repressed in most cells and conditions. eIF5A is linked to viral infection, aging, diabetes and neurodevelopmental disorders. Whilst derepression of the duplicated silent gene EIF5A2 is associated with several cancers, promoting metastasis. To expand our knowledge of eIF5As function, we searched for suppressors of yeast temperature-sensitive mutants of TIF51A, which cannot grow at restrictive temperature. All suppressors contained mutations in the transcriptional repressors Rox1 and Mot3, resulting in the upregulation of the paralogous gene TIF51B. Next, we searched for suppressors of TIF51A temperature-sensitive mutants in yeast lacking the TIF51B gene. The frequency of suppression was 20-times lower and all suppressors were revertants or contained intragenic mutations in the Tif51A protein that conferred stability. Our results suggest that the duplicated eIF5A gene serves as a non-conventional backup system that rescues mutations in the first copy, but acting at the population level. Furthermore, our results expand our understanding of the repression mechanisms that keep the second eIF5A gene silent. Lastly, our results demonstrate that eIF5A is an indispensable protein in eukaryotic cells, whose function cannot be substituted by mutations in other proteins or pathways. Article summaryeIF5A is an evolutionary conserved protein encoded by two paralogous genes in eukaryotes: one highly expressed and essential, and the other silent. eIF5A promotes translation elongation, and its deficiency is linked to diabetes, aging and neurodevelopmental disorders; while derepression of the silent gene promotes metastatic cancers. We isolated suppressors of conditional mutants of the first eIF5A gene in yeast cells. Suppressors either up-regulated the second eIF5A gene or reverted first copy mutations, restoring eIF5A protein levels and survival. Our work deepens our understanding of the eIF5A paralogue gene repression, and demonstrates that eIF5A is an indispensable protein for eukaryotic cells.