Eukaryotic Initiation Factor 5A Dephosphorylation is Required for Translational Arrest in Stationary Phase Cells

The protein known as eukaryotic initiation factor 5A (eIF5A) has an elusive role in translation. It has a unique and essential hypusine modification in a conserved lysine residue in most eukaryotes. In addition, this protein is modified by phosphorylation with unknown functions. Here we show that a phosphorylated state of eIF5A predominates in exponentially growing Trypanosoma cruzi cells and extensive dephosphorylation occurs in cells in stationary phase. Phosphorylation occurs mainly at Ser 2, as shown in yeast eIF5A. In addition, a novel phosphorylation site was identified at Tyr 21. In exponential cells, T. cruzi eIF5A is partially associated with polysomes, compatible with a proposed function as an elongation factor, and becomes relatively enriched in polysomal fractions in stationary phase. Overexpression of the wild type eIF5A, or eIF5A with Ser 2 replaced by Asp, but not by Ala, increases the rate of cell proliferation and protein synthesis. However, the presence of Asp instead of Ser 2 is toxic for cells reaching the stationary phase, which show a less pronounced protein synthesis arrest and a decreased amount of eIF5A in dense fractions of sucrose gradients. We conclude that eIF5A phosphorylation and dephosphorylation cycles regulate translation according to the growth conditions.

Source: BJ Cell - January 31, 2013 Category: Biochemistry Authors: J Chung, A Augusto Rocha, R Rosito Tonelli, B Amaral Castilho, S Schenkman Tags: BJ Signal Source Type: research