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. 2017 Apr 20;66(2):194-205.e5.
doi: 10.1016/j.molcel.2017.03.003. Epub 2017 Apr 6.

eIF5A Functions Globally in Translation Elongation and Termination

Anthony P Schuller  1 , Colin Chih-Chien Wu  1 , Thomas E Dever  2 , Allen R Buskirk  1 , Rachel Green  3
Affiliations

eIF5A Functions Globally in Translation Elongation and Termination

Anthony P Schuller et al. Mol Cell. .

Abstract

The eukaryotic translation factor eIF5A, originally identified as an initiation factor, was later shown to promote translation elongation of iterated proline sequences. Using a combination of ribosome profiling and in vitro biochemistry, we report a much broader role for eIF5A in elongation and uncover a critical function for eIF5A in termination. Ribosome profiling of an eIF5A-depleted strain reveals a global elongation defect, with abundant ribosomes stalling at many sequences, not limited to proline stretches. Our data also show ribosome accumulation at stop codons and in the 3' UTR, suggesting a global defect in termination in the absence of eIF5A. Using an in vitro reconstituted translation system, we find that eIF5A strongly promotes the translation of the stalling sequences identified by profiling and increases the rate of peptidyl-tRNA hydrolysis more than 17-fold. We conclude that eIF5A functions broadly in elongation and termination, rationalizing its high cellular abundance and essential nature.

Keywords: biochemistry; eIF5A; ribosome profiling; translation elongation; translation termination.

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Figures

Figure 1
Figure 1. Polar Distribution of Ribosomes toward 5′ End of Genes in eIF5Ad Cells
(A) Average ribosome occupancy from all genes aligned at start codons for WT (black line) and eIF5Ad cells (orange line) with schematic depicting queuing of ribosomes upstream of a paused ribosome (colored orange). Ribosome occupancy was normalized to show a mean value of 1 for each codon. (B) Example of ribosome occupancy along CHC1 gene in WT.1 (black) and eIF5Ad.1 (orange) cells. Rpm, reads per million. (C) Distributions of polarity scores for 4,946 genes from WT and eIF5Ad cells are plotted, for genes with at least 64 reads per dataset in ORFs (top panel). Schematic representation of polarity score (bottom panel). (D) Distributions of polarity scores for genes containing Pro-Pro dipeptide motifs (green) and genes lacking these motifs (brown) in eIF5Ad cells. WT distribution (includes both PP and non-PP) is included for reference (dotted). Numbers in parentheses denote the gene numbers included in the analysis. See also Figures S1 and S2.
Figure 2
Figure 2. eIF5A Alleviates Ribosome Pausing at More Than Poly-Pro Motifs
(A) Average ribosome occupancy centered at diproline motifs with the underlined Pro in the P site of the ribosome. Excluding motifs in genes with less than 64 reads per dataset in ORFs, 5,920 and 5,939 positions are averaged in WT and eIF5Ad, respectively. Arrow indicates stacked ribosomes. (B) Similar to (A), average plot centered at triproline motifs with underlined Pro in the E site of the ribosome. Inset: close-up view of the ribosome occupancy 10–50 nt downstream of the triproline motif. (C) Ribosome footprints on THO1 and PCL6 genes in WT.1 (black) and eIF5Ad.1 (orange) cells. Motifs of highest ribosome pausing are denoted. Rpm, reads per million. (D) Peptide motif associated with ribosome pausing in eIF5Ad cells, using motifs with pause score greater than 10 and weighted by pause score ratio of eIF5Ad/WT. Top 29 motifs are listed. (E) Average ribosome occupancy centered at 5,478 pause sites that match the 18 non-Pro-Pro pausing motifs identified in eIF5Ad cells. See also Figure S3.
Figure 3
Figure 3. eIF5A Stimulates Translation of Stalling Motifs In Vitro
(A) Schematic representation of in vitro elongation reactions using reconstituted translation system. Pelleted 80S initiation complexes are incubated with elongation factors, aminoacyl-tRNAs, GTP, ATP, and eIF5A. Reactions are quenched with KOH and peptide products resolved by electrophoretic TLCs. (B) Elongation kinetics for Phe-Phe- and Pro-Pro-containing peptides (MFFK and MPPK) in the presence and absence of eIF5A and hypusination modification. (C) Representative TLCs for elongation kinetics of dipeptide stalling motifs Asp-Asp (MDDK) and Asp-Pro (MDPK). (D) Comparison of elongation endpoints for all peptides analyzed in presence and absence of eIF5A. Error bars represent the standard deviation from three replicate experiments. See also Figure S4.
Figure 4
Figure 4. Hypusine Is Required for Polypro-line Elongation In Vitro
(A–D) Translation elongation kinetics for the following tripeptide motifs in the presence and absence of eIF5A and hypusination modification: (A) Phe-Phe-Phe (MFFFK), (B) Pro-Pro-Pro (MPPPK), (C) Pro-Asp-Ile (MPDIK), (D) Asp-Asp-Ile (MDDIK). Time points were quantified and reaction progression fitted to a single exponential. See also Figure S4.
Figure 5
Figure 5. Ribosomes Accumulate at Stop Codons and in 3′ UTRs in eIF5Ad Cells
(A) Metagene analysis of translation termination. Average ribosome occupancy from all genes aligned at their stop codons for WT and eIF5Ad cells. Arrow denotes stacked ribosomes ~30 nt upstream the stop codon peak. (B) Overlay and close-up view of (A), showing accumulated ribosomes in 3′ UTRs in eIF5Ad cells. (C) Similar to (A), metagene plot of stop codons for WT and eIF5Ad lysates treated with high-salt buffer. (D) Similar to (B), close-up view of 3′ UTR regions for WT and eIF5Ad lysates after high-salt wash. See also Figure S5.
Figure 6
Figure 6. eIF5A Stimulates eRF1-Mediated Peptidyl Hydrolysis
(A) Schematic for in vitro termination assays. Met-Phe-Lys elongation complexes containing an A-site stop codon (UAA) are reacted with eRF1:eRF3:GTP in the presence and absence of eIF5A. Time points are quenched with formic acid, peptide products resolved by electrophoretic TLCs, and rates quantified. (B) Rates of peptidyl hydrolysis by eRF1:eRF3 in presence and absence of eIF5A and hypusination modification. Error bars represent the standard deviation from at least three replicate experiments. See also Figures S6 and S7.
Figure 7
Figure 7. eIF5A Has a More General Role Than EFP
(A) Metagene analysis of translation termination for WT and Δefp E. coli cells shows neither stacked ribosomes (~30 nt upstream of stop codons) nor 3′ UTR ribosomes. (B) Comparison of tripeptide pausing in WT and Δefp E. coli cells. Pause scores of tripeptide motifs are plotted using E. coli WT and Δefp datasets (Woolstenhulme et al., 2015). Motifs with fewer than 30 occurrences in E. coli transcriptome are excluded from the analysis. Each dot represents one tripeptide motif; 6,018 motifs are included. Motifs with pause score higher than 8 are labeled. The diagonal line indicates the distribution expected for no enrichment. (C) Comparison of tripeptide pausing in WT and eIF5Ad cells. Pause scores of 6,022 tripeptide motifs (Table S1) are plotted for WT and eIF5Ad cells, for motifs with more than 100 occurrences in yeast transcriptome. Ten tripeptide motifs with highest pause scores upon eIF5A depletion are labeled. The diagonal line indicates the distribution expected for no enrichment. (D) Distributions of polarity scores for 2,186 genes from WT and Δefp E. coli cells are plotted, showing no significant difference. See also Figures S2 and S3.
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Comment in

  • Breaking the Silos of Protein Synthesis.
    Mateyak MK, Kinzy TG. Mateyak MK, et al. Trends Biochem Sci. 2017 Aug;42(8):587-588. doi: 10.1016/j.tibs.2017.06.006. Epub 2017 Jun 29. Trends Biochem Sci. 2017. PMID: 28669455 Free PMC article.

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