Abstract
BackgroundSaccharomyces cerevisiae is well-known as an ideal model system for basic research and important industrial microorganism for biotechnological applications. Acetic acid is an important growth inhibitor that has deleterious effects on both the growth and fermentation performance of yeast cells. Comprehensive understanding of the mechanisms underlying S. cerevisiae adaptive response to acetic acid is always a focus and indispensable for development of robust industrial strains. eIF5A is a specific translation factor that is especially required for the formation of peptide bond between certain residues including proline regarded as poor substrates for slow peptide bond formation. Decrease of eIF5A activity resulted in temperature-sensitive phenotype of yeast, while up-regulation of eIF5A protected transgenic Arabidopsis against high temperature, oxidative or osmotic stress. However, the exact roles and functional mechanisms of eIF5A in stress response are as yet largely unknown.ResultsIn this research, we compared cell growth between the eIF5A overexpressing and the control S. cerevisiae strains under various stressed conditions. Improvement of acetic acid tolerance by enhanced eIF5A activity was observed all in spot assay, growth profiles and survival assay. eIF5A prompts the synthesis of Ume6p, a pleiotropic transcriptional factor containing polyproline motifs, mainly in a translational related way. As a consequence, BEM4, BUD21 and IME4, the direct targets of Ume6p, were up-regulated in eIF5A overexpressing strain, especially under acetic acid stress. Overexpression of UME6 results in similar profiles of cell growth and target genes transcription to eIF5A overexpression, confirming the role of Ume6p and its association between eIF5A and acetic acid tolerance.ConclusionTranslation factor eIF5A protects yeast cells against acetic acid challenge by the eIF5A-Ume6p-Bud21p/Ime4p/Bem4p axles, which provides new insights into the molecular mechanisms underlying the adaptive response and tolerance to acetic acid in S. cerevisiae and novel targets for construction of robust industrial strains.
Highlights
Saccharomyces cerevisiae is well-known as an ideal model system for basic research and important industrial microorganism for biotechnological applications
The hypusine modification of eIF5A involves two enzymatic reactions, in which deoxyhypusine synthase (DHS) catalyzes the transfer of a n-butylamine moiety from the polyamine spermidine to one specific lysine residue of the eIF5A precursor to form deoxyhypusine intermediate, deoxyhypusine hydroxylase (DOHH) catalyzes the hydroxylation of deoxyhypusine to form hypusinecontaining, biologically active eIF5A [4, 6]. Both eIF5A precursor and its hypusine modification are highly conserved and essential in all archaea and eukaryotes, suggesting the importance of active eIF5A in these organisms [5,6,7,8,9,10,11,12,13]. eIF5A was initially characterized to function in initiation of protein synthesis for its ability to stimulate the synthesis of methionyl-puromycin, a model reaction indicating the synthesis of the first peptide bond [1,2,3]
Overexpression of eIF5A enhances acetic acid tolerance of yeast cells Cell growth of yeast strains overexpressing HYP2, DYS1 or LIA1 on synthetic complete medium SC medium without uracil (SC-Ura) under various stress conditions were compared with the control strain by spot assay first
Summary
Saccharomyces cerevisiae is well-known as an ideal model system for basic research and important industrial microorganism for biotechnological applications. The hypusine modification of eIF5A involves two enzymatic reactions, in which deoxyhypusine synthase (DHS) catalyzes the transfer of a n-butylamine moiety from the polyamine spermidine to one specific lysine residue of the eIF5A precursor to form deoxyhypusine intermediate, deoxyhypusine hydroxylase (DOHH) catalyzes the hydroxylation of deoxyhypusine to form hypusinecontaining, biologically active eIF5A [4, 6] Both eIF5A precursor and its hypusine modification are highly conserved and essential in all archaea and eukaryotes, suggesting the importance of active eIF5A in these organisms [5,6,7,8,9,10,11,12,13]. The precise relations between the activity of eIF5A and the specialized target proteins, and their physiological roles remain elusive and need to be further elucidated
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