scholarly journals Overlapping regions of Caf20 mediate its interactions with the mRNA-5′cap-binding protein eIF4E and with ribosomes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ebelechukwu C. Nwokoye ◽  
Eiman AlNaseem ◽  
Robert A. Crawford ◽  
Lydia M. Castelli ◽  
Martin D. Jennings ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Selection Process ◽  
Critical Role ◽  
Interaction Region ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Ribosome Binding ◽  
Binding Interface ◽  
The Family ◽  
Canonical Motif

AbstractBy interacting with the mRNA 5′ cap, the translation initiation factor eIF4E plays a critical role in selecting mRNAs for protein synthesis in eukaryotic cells. Caf20 is a member of the family of proteins found across eukaryotes termed 4E-BPs, which compete with eIF4G for interaction with eIF4E. Caf20 independently interacts with ribosomes. Thus, Caf20 modulates the mRNA selection process via poorly understood mechanisms. Here we performed unbiased mutagenesis across Caf20 to characterise which regions of Caf20 are important for interaction with eIF4E and with ribosomes. Caf20 binding to eIF4E is entirely dependent on a canonical motif shared with other 4E-BPs. However, binding to ribosomes is weakened by mutations throughout the protein, suggesting an extended binding interface that partially overlaps with the eIF4E-interaction region. By using chemical crosslinking, we identify a potential ribosome interaction region on the ribosome surface that spans both small and large subunits and is close to a known interaction site of eIF3. The function of ribosome binding by Caf20 remains unclear.

scholarly journals Polyribosome Binding by GCN1 Is Required for Full Activation of Eukaryotic Translation Initiation Factor 2α Kinase GCN2 during Amino Acid Starvation

2005 ◽  
Vol 280 (16) ◽  
pp. 16514-16521 ◽  
Author(s):  
Evelyn Sattlegger ◽  
Alan G. Hinnebusch
Keyword(s):  
Amino Acid ◽  
Translation Initiation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Translation Initiation Factor ◽  
Control Of Gene Expression ◽  
Eukaryotic Translation ◽  
Ribosome Binding ◽  
Cell Extracts ◽  
Eukaryotic Translation Initiation

The protein kinase GCN2 mediates translational control of gene expression in amino acid-starved cells by phosphorylating eukaryotic translation initiation factor 2α. InSaccharomyces cerevisiae,activation of GCN2 by uncharged tRNAs in starved cells requires its direct interaction with both the GCN1·GCN20 regulatory complex and ribosomes. GCN1 also interacts with ribosomes in cell extracts, but it was unknown whether this activity is crucial for its ability to stimulate GCN2 function in starved cells. We describe point mutations in two conserved, noncontiguous segments of GCN1 that lead to reduced polyribosome association by GCN1·GCN20 in living cells without reducing GCN1 expression or its interaction with GCN20. Mutating both segments simultaneously produced a greater reduction in polyribosome binding by GCN1·GCN20 and a stronger decrease in eukaryotic translation initiation factor 2α phosphorylation than did mutating in one segment alone. These findings provide strong evidence that ribosome binding by GCN1 is required for its role as a positive regulator of GCN2. A particular mutation in the GCN1 domain, related in sequence to translation elongation factor 3 (eEF3), decreased GCN2 activation much more than it reduced ribosome binding by GCN1. Hence, the eEF3-like domain appears to have an effector function in GCN2 activation. This conclusion supports the model that an eEF3-related activity of GCN1 influences occupancy of the ribosomal decoding site by uncharged tRNA in starved cells.

scholarly journals Eukaryotic translation initiation factor 3 plays distinct roles at the mRNA entry and exit channels of the ribosomal preinitiation complex

2016 ◽  
Author(s):  
Colin Echeverría Aitken ◽  
Petra Beznosková ◽  
Vladislava Vlčkova ◽  
Wen-Ling Chiu ◽  
Fujun Zhou ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Critical Role ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Translation Initiation Factor ◽  
Eukaryotic Translation ◽  
Functional Variants ◽  
Eukaryotic Translation Initiation ◽  
Translation Initiation Factor 3

AbstractEukaryotic translation initiation factor 3 (eIF3) is a central player in recruitment of the pre-initiation complex (PIC) to mRNA. We probed the effects on mRNA recruitment of a library of S. cerevisiae eIF3 functional variants spanning its 5 essential subunits using an in vitro-reconstituted system. Mutations throughout eIF3 disrupt its interaction with the PIC and diminish its ability to accelerate recruitment to a native yeast mRNA. Alterations to the eIF3a CTD and eIF3b/i/g significantly slow mRNA recruitment, and mutations within eIF3b/i/g destabilize eIF2·GTP·Met-tRNAi binding to the PIC. Using model mRNAs lacking contacts with the 40S entry or exit channels, we uncover a critical role for eIF3 requiring the eIF3a NTD, in stabilizing mRNA interactions at the exit channel, and an ancillary role at the entry channel requiring residues of the eIF3a CTD. These functions are redundant: defects at each channel can be rescued by filling the other channel with mRNA.

scholarly journals Eukaryotic translation initiation factor 3 plays distinct roles at the mRNA entry and exit channels of the ribosomal preinitiation complex

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Colin Echeverría Aitken ◽  
Petra Beznosková ◽  
Vladislava Vlčkova ◽  
Wen-Ling Chiu ◽  
Fujun Zhou ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Critical Role ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Translation Initiation Factor ◽  
Eukaryotic Translation ◽  
Functional Variants ◽  
Eukaryotic Translation Initiation ◽  
Translation Initiation Factor 3

Eukaryotic translation initiation factor 3 (eIF3) is a central player in recruitment of the pre-initiation complex (PIC) to mRNA. We probed the effects on mRNA recruitment of a library of S. cerevisiae eIF3 functional variants spanning its 5 essential subunits using an in vitro-reconstituted system. Mutations throughout eIF3 disrupt its interaction with the PIC and diminish its ability to accelerate recruitment to a native yeast mRNA. Alterations to the eIF3a CTD and eIF3b/i/g significantly slow mRNA recruitment, and mutations within eIF3b/i/g destabilize eIF2•GTP•Met-tRNAi binding to the PIC. Using model mRNAs lacking contacts with the 40S entry or exit channels, we uncovered a critical role for eIF3 requiring the eIF3a NTD, in stabilizing mRNA interactions at the exit channel, and an ancillary role at the entry channel requiring residues of the eIF3a CTD. These functions are redundant: defects at each channel can be rescued by filling the other channel with mRNA.

scholarly journals Back to translation: removal of aIF2 from the 5′-end of mRNAs by translation recovery factor in the crenarchaeon Sulfolobus solfataricus

2013 ◽  
Vol 42 (4) ◽  
pp. 2505-2511 ◽  
Author(s):  
Birgit Märtens ◽  
Salim Manoharadas ◽  
David Hasenöhrl ◽  
Lukas Zeichen ◽  
Udo Bläsi
Keyword(s):  
Stationary Phase ◽  
Translation Initiation ◽  
Sulfolobus Solfataricus ◽  
Growth Conditions ◽  
Translation Initiation Factor ◽  
Recovery Factor ◽  
Initiation Factor ◽  
Ribosome Binding ◽  
Γ Subunit

Abstract The translation initiation factor aIF2 of the crenarchaeon Sulfolobus solfataricus (Sso) recruits initiator tRNA to the ribosome and stabilizes mRNAs by binding via the γ-subunit to their 5′-triphosphate end. It has been hypothesized that the latter occurs predominantly during unfavorable growth conditions, and that aIF2 or aIF2-γ is released on relief of nutrient stress to enable in particular anew translation of leaderless mRNAs. As leaderless mRNAs are prevalent in Sso and aIF2-γ bound to the 5′-end of a leaderless RNA inhibited ribosome binding in vitro, we aimed at elucidating the mechanism underlying aIF2/aIF2-γ recycling from mRNAs. We have identified a protein termed Trf (translation recovery factor) that co-purified with trimeric aIF2 during outgrowth of cells from prolonged stationary phase. Subsequent in vitro studies revealed that Trf triggers the release of trimeric aIF2 from RNA, and that Trf directly interacts with the aIF2-γ subunit. The importance of Trf is further underscored by an impaired protein synthesis during outgrowth from stationary phase in a Sso trf deletion mutant.

scholarly journals Specific Isoforms of Translation Initiation Factor 4GI Show Differences in Translational Activity

2006 ◽  
Vol 26 (22) ◽  
pp. 8448-8460 ◽  
Author(s):  
Mark J. Coldwell ◽  
Simon J. Morley
Keyword(s):  
Translation Initiation ◽  
Hela Cells ◽  
Mammalian Cells ◽  
Critical Role ◽  
Translation Initiation Factor ◽  
Protein Isoforms ◽  
Initiation Factor ◽  
Functional Studies ◽  
Eif2α Phosphorylation ◽  
Translational Activity

ABSTRACT The eukaryotic initiation factor (eIF) 4GI gene locus (eIF4GI) contains three identified promoters, generating alternately spliced mRNAs, yielding a total of five eIF4GI protein isoforms. Although eIF4GI plays a critical role in mRNA recruitment to the ribosomes, little is known about the functions of the different isoforms, their partner binding capacities, or the role of the homolog, eIF4GII, in translation initiation. To directly address this, we have used short interfering RNAs (siRNAs) expressed from DNA vectors to silence the expression of eIF4GI in HeLa cells. Here we show that reduced levels of specific mRNA and eIF4GI isoforms in HeLa cells promoted aberrant morphology and a partial inhibition of translation. The latter reflected dephosphorylation of 4E-BP1 and decreased eIF4F complex levels, with no change in eIF2α phosphorylation. Expression of siRNA-resistant Myc-tagged eIF4GI isoforms has allowed us to show that the different isoforms exhibit significant differences in their ability to restore translation rates. Here we quantify the efficiency of eIF4GI promoter usage in mammalian cells and demonstrate that even though the longest isoform of eIF4GI (eIF4GIf) was relatively poorly expressed when reintroduced, it was more efficient at promoting the translation of cellular mRNAs than the more highly expressed shorter isoforms used in previous functional studies.

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