Several translation factor that act in different steps of translation are conserved through evolution. Among them, the putative eukaryotic translation initiation factor 5A (eIF5A), is a small acid protein with 17KDa, highly conserved and essential from arqueas to eukaryotes. Despite its involvement with the initiation step of translation has never been described, eIF5A has been observed associated with translation activated ribosomes and its mutants clearly demonstrates defects at the total protein synthesis (JAO and CHEN 2006; ZANELLI et al. 2006; DIAS et al. 2008).. Interestingly, the polysome profile defects of temperature sensitive eIF5A mutants suggest a role at the elongation step of translation instead of initiation (ZANELLI et al. 2006; GREGIO et al. 2009; SAINI et al. 2009). eIF5A is the only protein known to contain the essential amino acid residue hypusine, generated through a posttranslational modification, dependent on the polyamine spermidine, known as hypusination. This modification occurs in two steps: initially, the enzyme deoxyhypusine synthase (DYS1) transfers the aminobutyl moiety from the polyamine spermidine to the amino group of one specific eIF5A lysine residue (K51) to form deoxyhypusine. Then, a second enzyme, deoxyhypusine hydroxylase, adds a hydroxyl group to deoxyhypusine forming the hypusine residue. Finally, a structural analogue of the polyamine spermidine, known as GC7, has already been described as an inhibitor of eIF5A posttranslational modification and its function. However, GC7 interferes with other cellular processes, as translation initiation, activation of cellular stress response and others (Landau et al., 2010). Because of that, GC7 does not demonstrate specificity and this might be the reason of its toxicity. So, defining GC7 cellular targets will allow the evaluation of its hypusination specificity and the cellular toxicity observed.
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