Genetic Interactions of Yeast Eukaryotic Translation Initiation Factor 5A (eIF5A) Reveal Connections to Poly(A)-Binding Protein and Protein Kinase C Signaling

Abstract The highly conserved eukaryotic translation initiation factor eIF5A has been proposed to have various roles in the cell, from translation to mRNA decay to nuclear protein export. To further our understanding of this essential protein, three temperature-sensitive alleles of the yeast TIF51A gene have been characterized. Two mutant eIF5A proteins contain mutations in a proline residue at the junction between the two eIF5A domains and the third, strongest allele encodes a protein with a single mutation in each domain, both of which are required for the growth defect. The stronger tif51A alleles cause defects in degradation of short-lived mRNAs, supporting a role for this protein in mRNA decay. A multicopy suppressor screen revealed six genes, the overexpression of which allows growth of a tif51A-1 strain at high temperature; these genes include PAB1, PKC1, and PKC1 regulators WSC1, WSC2, and WSC3. Further results suggest that eIF5A may also be involved in ribosomal synthesis and the WSC/PKC1 signaling pathway for cell wall integrity or related processes.

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mRNA Decapping in Yeast Requires Dissociation of the Cap Binding Protein, Eukaryotic Translation Initiation Factor 4E

Molecular and Cellular Biology ◽

10.1128/mcb.20.21.7933-7942.2000 ◽

2000 ◽

Vol 20 (21) ◽

pp. 7933-7942 ◽

Cited By ~ 99

Author(s):

David C. Schwartz ◽

Roy Parker

Keyword(s):

Translation Initiation ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Mrna Turnover ◽

Temperature Sensitive ◽

Eukaryotic Translation Initiation Factor ◽

Eukaryotic Translation ◽

Eukaryotic Translation Initiation ◽

Sensitive Allele

ABSTRACT A major pathway of eukaryotic mRNA turnover occurs by deadenylation-dependent decapping that exposes the transcript to 5′→3′ exonucleolytic degradation. A critical step in this pathway is decapping, since removal of the cap structure permits 5′→3′ exonucleolytic digestion. Based on alterations in mRNA decay rate from strains deficient in translation initiation, it has been proposed that the decapping rate is modulated by a competition between the cytoplasmic cap binding complex, which promotes translation initiation, and the decapping enzyme, Dcp1p. In order to test this model directly, we examined the functional interaction of Dcp1p and the cap binding protein, eukaryotic translation initiation factor 4E (eIF4E), in vitro. These experiments indicated that eIF4E is an inhibitor of Dcp1p in vitro due to its ability to bind the 5′ cap structure. In addition, we demonstrate that in vivo a temperature-sensitive allele of eIF4E (cdc33-42) suppressed the decapping defect of a partial loss-of-function allele of DCP1. These results argue that dissociation of eIF4E from the cap structure is required before decapping. Interestingly, the temperature-sensitive allele of eIF4E does not suppress the decapping defect seen in strains lacking the decapping activators, Lsm1p and Pat1p. This indicates that these activators of decapping affect a step in mRNA turnover distinct from the competition between Dcp1 and eIF4E.

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Eukaryotic Translation Initiation Factor 4E-Dependent Translation Is Not Essential for Survival of Starved Yeast Cells

Journal of Bacteriology ◽

10.1128/jb.183.15.4477-4483.2001 ◽

2001 ◽

Vol 183 (15) ◽

pp. 4477-4483 ◽

Cited By ~ 16

Author(s):

Irit Paz ◽

Mordechai Choder

Keyword(s):

Translation Initiation ◽

Translation Initiation Factor ◽

Yeast Cells ◽

Initiation Factor ◽

Heat Inactivation ◽

Temperature Sensitive ◽

Eukaryotic Translation Initiation Factor ◽

Eukaryotic Translation ◽

Eukaryotic Mrnas ◽

Eukaryotic Translation Initiation

ABSTRACT The eukaryotic translation initiation factor 4E (eIF4E) interacts with the mRNA 5′ cap structure (m7GpppX) and is essential for the appropriate translation of the vast majority of eukaryotic mRNAs. Most studies of the yeastSaccharomyces cerevisiae CDC33 gene product, eIF4E, have been carried out with logarithmically growing cells, and little is known about its role in starved, nonproliferating cells that enter the stationary phase (SP). It has previously been found that the rate of translation in SP cells is more than 2 orders of magnitude lower than it is in dividing yeast cells. Here we show that this low rate of translation is essential for maintaining the viability of starved yeast cells that enter SP. Specifically, starved cells whose eIF4A is inactive or treated with cycloheximide rapidly lose viability. Moreover, after heat inactivation of the cdc33temperature-sensitive product, the synthesis of most proteins is abolished and only a small group of proteins is still produced. Unexpectedly, starved cdc33 mutant cells whose eIF4E is inactive and which therefore fail to synthesize the bulk of their proteins remain viable for long periods of time, indistinguishable from their isogenic wild-type counterparts. Taken together, our results indicate that eIF4E-independent translation is necessary and sufficient for survival of yeast cells during long periods of starvation.

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