{"gene":"EIF5","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":1994,"finding":"eIF5 forms a specific complex with eIF2 in a 1:1 stoichiometry (apparent Mr ~160 kDa), and this interaction is required for eIF5 to catalyze hydrolysis of GTP bound to the 40S initiation complex and promote 80S initiation complex formation.","method":"Glycerol gradient sedimentation, in vitro GTPase assay with purified recombinant eIF5","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified proteins, replicated in multiple subsequent studies","pmids":["8161539"],"is_preprint":false},{"year":1998,"finding":"eIF5 stably associates with the yeast eIF3 core complex (composed of Tif32p/eIF3a, Nip1p/eIF3c, Prt1p/eIF3b, Tif34p/eIF3i, Tif35p/eIF3g); Nip1p/eIF3c directly binds eIF5 in two-hybrid and in vitro binding assays.","method":"Ni2+ affinity purification of His-Prt1p complex, mass spectrometry, yeast two-hybrid, in vitro protein binding","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (affinity purification, MS, two-hybrid, in vitro binding), replicated in subsequent studies","pmids":["9671501"],"is_preprint":false},{"year":2000,"finding":"eIF5 bridges interaction between eIF3 (via NIP1/eIF3c N-terminus) and eIF2 (via eIF2β N-terminal half) through a conserved bipartite motif in the eIF5 C-terminal domain (CTD), forming a multifactor complex (MFC) that also contains eIF1 and initiator tRNA(Met) in vivo. The tif5-7A mutation in the bipartite motif disrupts MFC assembly and causes temperature-sensitive growth and reduction in translation initiation.","method":"In vitro protein binding, co-immunoprecipitation from yeast cell extracts, genetic analysis (tif5-7A mutant)","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays plus in vivo MFC disruption phenotype, replicated across labs","pmids":["11018020"],"is_preprint":false},{"year":2000,"finding":"The C-terminus of eIF5 (glutamic acid-rich bipartite motif) is required for interaction with the β subunit of eIF2; alanine substitution of conserved glutamic acid residues (E346A/E347A and E384A/E385A) abolishes eIF5–eIF2β binding, GTP hydrolysis, 80S initiation complex formation, and in vivo cell viability.","method":"Deletion and alanine substitution mutagenesis, in vitro binding assays, GTPase assay, yeast complementation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis with multiple orthogonal functional assays (binding, GTPase, 80S formation, in vivo rescue)","pmids":["10805737"],"is_preprint":false},{"year":2001,"finding":"eIF5 acts as a classical GTPase-activating protein (GAP) for eIF2: its interaction with eIF2 is enhanced by AlF4- (mimicking the transition state), and it contains an 'arginine finger' (Arg15) flanked by hydrophobic residues; mutation R15M abolishes both GTP hydrolysis stimulation and in vitro mRNA translation. Arg48 also contributes to the GTPase active site.","method":"AlF4- binding assay, site-directed mutagenesis (R15M, R48M), in vitro GTPase assay, in vitro translation assay","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of catalytic residues with multiple functional readouts, replicated mechanistically","pmids":["11166181"],"is_preprint":false},{"year":2001,"finding":"The eIF5-CTD simultaneously binds eIF4G (cap-binding complex subunit) and eIF3/NIP1, suggesting it bridges the cap-binding complex to the PIC. In vivo, the tif5-7A mutation (disrupting MFC) eliminates eIF5 from the pre-initiation complex and causes accumulation of 48S complexes, indicating GTP hydrolysis/conversion of 48S to 80S is the rate-limiting step.","method":"In vitro protein binding, GST pulldown, polysome/ribosome sedimentation analysis, in vivo crosslinking","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (pulldown, sedimentation, in vivo), consistent with prior findings","pmids":["11331597"],"is_preprint":false},{"year":2003,"finding":"eIF5 makes critical contacts with the 40S ribosomal subunit in vivo, performing redundant functions with the TIF32-CTD of eIF3a for 40S binding. The TIF32-CTD binds helices 16–18 of 18S rRNA in vitro, and NIP1/eIF5 interact with 40S protein RPS0A.","method":"In vivo co-immunoprecipitation from yeast, in vitro RNA binding assay, deletion analysis","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two methods (in vivo IP, in vitro binding), single lab","pmids":["12651896"],"is_preprint":false},{"year":2003,"finding":"The eIF4G HEAT domain interacts with eIF5 (and eIF1); eIF1 binds simultaneously to eIF4G and eIF3c in vitro; mutations disrupting eIF4G–eIF5 interaction lead to elevated non-AUG initiation in vivo, indicating the eIF4G HEAT domain–eIF5/eIF1 interaction is important for scanning preinitiation complex integrity and AUG stringency.","method":"In vitro protein binding, two-hybrid, in vivo genetic suppression, reporter assay for non-AUG initiation","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods, single lab","pmids":["12861028"],"is_preprint":false},{"year":2004,"finding":"The N-terminal domain (NTD) of NIP1/eIF3c directly binds eIF1 and eIF5 to form the MFC; specific NIP1-NTD mutations reduce eIF1 or eIF5 binding, alter UUG start codon utilization (Sui- phenotype), and impair TC recruitment to 40S ribosomes. eIF1 overexpression suppresses the Sui- phenotype of both NIP1 and eIF5-G31R mutants, indicating that NIP1-NTD coordinates eIF1–eIF5 interaction to inhibit GTP hydrolysis at non-AUG codons.","method":"Site-directed mutagenesis of NIP1-NTD, yeast genetics (Sui- phenotype assay), in vitro binding, eIF1/eIF5 overexpression suppression","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (mutagenesis, genetics, binding assays), consistent mechanistic model","pmids":["15485912"],"is_preprint":false},{"year":2006,"finding":"Crystal structure of the human eIF5-CTD at high resolution shows it is exclusively α-helical and homologous to the eIF2Bε-CTD (W2/HEAT domain). The binding sites for eIF2β, eIF3c, and eIF1 were mapped onto the structure: eIF2β and eIF3c bind non-overlapping patches of negative and positive electrostatic potential, respectively.","method":"X-ray crystallography (crystal structure), electrostatic surface analysis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution crystal structure with functional site mapping, independently confirmed by S. cerevisiae structure","pmids":["16781736"],"is_preprint":false},{"year":2006,"finding":"Crystal structure of the S. cerevisiae eIF5-CTD at 1.5 Å confirms it contains an atypical HEAT motif; surface analysis identifies conserved potential interaction regions for partner eIFs.","method":"X-ray crystallography","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure at 1.5 Å resolution, consistent with human eIF5-CTD structure","pmids":["16616930"],"is_preprint":false},{"year":2007,"finding":"eIF1 has two distinct eIF5-binding faces: its N-terminal tail and a basic/hydrophobic surface (KH region). Mutation of the KH region is lethal and causes dominant relaxation of start codon selection. The eIF1 N-terminal tail plays a stimulatory role in cooperative MFC assembly.","method":"NMR solution structure of yeast eIF1 used for interface mapping, yeast two-hybrid, in vitro binding, genetic analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR-guided mutagenesis with in vitro and in vivo functional validation","pmids":["17974565"],"is_preprint":false},{"year":2010,"finding":"eIF5 has a GDP dissociation inhibitor (GDI) activity distinct from its GAP function: it stabilizes GDP binding to eIF2 between rounds of initiation. Conserved residues in eIF5 are required specifically for GDI (not GAP) activity. eIF5 is also a critical component of the eIF2(αP) regulatory complex that inhibits eIF2B GEF activity.","method":"Fluorescence nucleotide binding assays, mutagenesis of eIF5 GDI-specific residues, genetic assays (GCN4 translational control), in vitro GEF inhibition assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal in vitro assays plus genetic validation, published in Nature","pmids":["20485439"],"is_preprint":false},{"year":2013,"finding":"eIF2B acts as a GDI displacement factor (GDF) that recruits eIF2 from the eIF2•GDP/eIF5 GDI complex prior to GEF action; GDF activity depends on eIF2Bε and eIF2Bγ subunits and is insensitive to eIF2α phosphorylation (unlike GEF). eIF2B GDF and GEF activities are independent.","method":"Protein-protein interaction assays, fluorescent nucleotide exchange kinetic assays, mutagenesis of eIF2B subunits","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — kinetic assays with purified factors, mutagenesis separating GDF from GEF function","pmids":["24352424"],"is_preprint":false},{"year":2013,"finding":"Upon AUG codon recognition, the C-terminal tail (CTT) of eIF1A moves closer to the eIF5 NTD; this movement is coupled to eIF1 dissociation from the PIC. eIF1 dissociation plus eIF1A-CTT movement toward eIF5 is required to trigger Pi release from eIF2•GDP•Pi. The eIF5-CTD antagonizes eIF1 binding to the PIC.","method":"FRET-based distance measurements in reconstituted yeast PICs, mutagenesis, phosphate release assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — FRET in reconstituted system plus mutagenesis and phosphate release assays","pmids":["23293029"],"is_preprint":false},{"year":2014,"finding":"eIF5-G31R (Sui- mutation) alters Pi release: it accelerates Pi release at UUG codons and decreases it at AUG codons, stabilizing the closed PIC conformation at UUG. Suppressor G62S mitigates both defects; suppressor M18V primarily impairs GTP hydrolysis with little effect on PIC conformation, indicating eIF5 controls both Pi release and open-to-closed PIC conformational transitions for accurate AUG selection.","method":"In vitro GTP hydrolysis assays, Pi release assays, FRET-based PIC conformation assays, mutagenesis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple in vitro functional assays with systematic mutagenesis","pmids":["25114053"],"is_preprint":false},{"year":2014,"finding":"eIF5 and eIF5B together stimulate 48S initiation complex formation during ribosomal scanning; eIF5-induced hydrolysis of eIF2-bound GTP is essential for this stimulation, increasing the probability that scanning complexes arrest at non-optimal start codons. eIF5B then stabilizes the initiator tRNA in the P site after eIF2•GDP dissociation.","method":"In vitro 48S IC assembly assays, GTPase assays, mutagenesis of eIF1A and eIF5B","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro system with mutagenesis and multiple readouts","pmids":["25260592"],"is_preprint":false},{"year":2002,"finding":"Casein kinase II (CK II) phosphorylates mammalian eIF5 in vitro and in vivo at Ser-387 and Ser-388 near the C-terminus (within an acidic cluster), accounting for ~90% of total phosphorylation; a minor site is Ser-174. Alanine substitution at S387/S388 abolishes both in vitro and in vivo phosphorylation.","method":"Kinase isolation and biochemical characterization, mass spectrometry of phosphorylation sites, alanine substitution mutagenesis, in vivo 32P labeling","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — MS site mapping combined with mutagenesis and in vivo labeling","pmids":["11861906"],"is_preprint":false},{"year":2003,"finding":"In S. cerevisiae, eIF5 is phosphorylated in vivo on multiple serine residues by casein kinase II; phosphopeptide mapping reveals four major sites identical to in vitro CK II sites. However, Ser-to-Ala mutations at all five CK II consensus sites in eIF5 had no obvious effect on cell growth under normal conditions.","method":"In vivo 32P labeling and phosphopeptide mapping, conditional CK II mutant yeast strain, site-directed mutagenesis","journal":"Yeast","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo phosphorylation confirmed by multiple methods; functional significance unclear (negative growth result under normal conditions)","pmids":["12518314"],"is_preprint":false},{"year":2017,"finding":"The eIF3c N-terminal domain (NTD) is divided into 3c0, 3c1, and 3c2 sub-regions; 3c0 binds eIF5 strongly but only weakly to eIF1's ribosome-binding surface, while 3c1/3c2 form a stoichiometric complex with eIF1. The 3c0:eIF5 interaction stabilizes the scanning PIC by preventing the inhibitory 3c0:eIF1 interaction; upon start codon recognition, interactions involving eIF5 and ultimately 3c0:eIF1 facilitate eIF1 release.","method":"NMR, in vitro binding assays, mutagenesis of NIP1-NTD subregions","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural data combined with mutagenesis and binding assays","pmids":["28297669"],"is_preprint":false},{"year":2018,"finding":"Cryo-EM structure (3.0 Å) of a yeast 48S PIC shows the eIF5-NTD bound to the 40S subunit at the location vacated by eIF1; eIF5-NTD interacts with Met-tRNAi to allow a more accommodated (PIN) orientation. Substitutions of eIF5 residues at the eIF5-NTD/tRNAi interface influence initiation at near-cognate UUG codons in vivo and closed/open PIC conformation in vitro.","method":"Cryo-EM reconstruction, in vivo UUG initiation assays, in vitro PIC conformation assays, mutagenesis","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with mutagenesis and orthogonal functional assays","pmids":["30475211"],"is_preprint":false},{"year":2018,"finding":"Human eIF5 interacts with eIF5B via a C-terminal eIF5B-binding motif, competing with eIF1A for eIF5B binding with ~100-fold higher affinity than eIF1A; this interaction may coordinate start codon selection (eIF5 as GAP of eIF2) with ribosomal subunit joining (eIF5B), with eIF1A displacing eIF5 from eIF5B to allow the eIF5:eIF2-GDP complex to leave the ribosome.","method":"Binding affinity measurements (ITC/fluorescence), competition assays, identification of eIF5B-binding motif in eIF5","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative binding assays with motif identification, single lab","pmids":["30211544"],"is_preprint":false},{"year":2016,"finding":"eIF2β acts in concert with eIF5 to prevent premature GDP release from eIF2γ: a growth suppressor mutation in eIF2β specifically prevents eIF5 GDI from stabilizing GDP binding to eIF2 (increases GDP off-rate from eIF2•GDP/eIF5 complexes) without affecting intrinsic eIF2 affinities for GDP or initiator tRNA, impairing GCN4 translational control.","method":"Fluorescent nucleotide binding kinetics assays, genetic analysis (GCN4 derepression), mutagenesis of eIF2β","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — kinetic assays with purified factors plus genetic validation; delineates GDI mechanism","pmids":["27458202"],"is_preprint":false},{"year":2021,"finding":"Human eIF5 contains two intrinsically disordered regions (IDRs): the DWEAR motif and the C-terminal tail (CTT), which dynamically contact the folded CTD and compete with each other. CTD•CTT interaction favors eIF2β binding to eIF5-CTD, whereas CTD•DWEAR interaction favors eIF1A binding. CK2 phosphorylation significantly increases eIF5 affinity for eIF2; eIF2β has at least two (likely three) eIF5-binding sites.","method":"NMR spectroscopy, binding assays, phosphomimetic mutagenesis","journal":"Biophysical chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — NMR plus binding assays, single lab","pmids":["34923394"],"is_preprint":false},{"year":2022,"finding":"CK2 phosphorylation of eIF5 increases its affinity for eIF1A; a new contact interface was identified between eIF5-CTD and the OB domain of eIF1A. Dynamic intramolecular interactions within both eIF5 and eIF1A modulate this interaction.","method":"Binding assays, phosphomimetic mutagenesis of eIF5, NMR/structural analysis","journal":"Current research in structural biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — binding assays with mutagenesis, single lab; extends prior IDR findings","pmids":["36164648"],"is_preprint":false},{"year":2024,"finding":"eIF5 (via its GAP activity) preferentially stimulates poly-GA RAN translation from a CUG near-cognate start codon in C9orf72 FTLD/ALS; inactive eIF5 mutants do not stimulate. Mutation of the CUG to CCG or AUG abolishes the stimulatory effect. In a Drosophila C9orf72 model, knockdown of eIF5 reduces poly-GA expression in vivo.","method":"Transfection of WT and inactive eIF5 mutants, RAN translation reporters, codon mutation analysis, Drosophila RNAi knockdown","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (cell-based reporters, mutagenesis, in vivo Drosophila), single lab","pmids":["38301895"],"is_preprint":false},{"year":2024,"finding":"Single-molecule fluorescence analysis of human translation initiation showed that eIF5 only transiently binds initiation complexes late in initiation immediately prior to eIF5B association; eIF5 association requires a translation start site and is inhibited by alternative start sites. eIF1 and eIF5 have opposing roles during initiation (knockdown/overexpression experiments in human cells confirmed this).","method":"Single-molecule fluorescence (smFRET/TIRF) on reconstituted human PICs, knockdown and overexpression in human cells","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — single-molecule reconstitution plus cell validation; preprint, not yet peer-reviewed","pmids":["39026837"],"is_preprint":true},{"year":2025,"finding":"Crystal structure of yeast eIF5-CTD in complex with eIF2β K-box 3 reveals an extended binding site on eIF2β beyond the K-box. eIF2β has three distinct binding sites (one per K-box), and human eIF5, eIF2Bε, and 5MP1 can all bind to all three sites while reducing each other's affinities. CK2 phosphomimetic mutations in eIF5 increase affinities for all these partners, and eIF2B speeds dissociation of eIF5 from eIF2-GDP to promote nucleotide exchange.","method":"X-ray crystallography, NMR, binding assays with phosphomimetic mutants","journal":"RNA","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with NMR and quantitative binding assays, multiple orthogonal methods","pmids":["40670154"],"is_preprint":false},{"year":2012,"finding":"Sequential binding of eIF5-CTD to the eIF4G RS1 domain and eIF2β K-boxes stabilizes the 48S PIC and promotes its shift to initiation mode: eIF4G-RS1/eIF5-CTD interaction directly links eIF4G to the PIC to enhance mRNA binding; eIF2β-K-boxes increase mRNA binding in a manner reversed by eIF5-CTD; mutations in these interactions restore AUG selection accuracy impaired by an eIF2β mutation.","method":"In vitro 48S complex assembly, mRNA binding assays, in vivo start codon selection assays, mutagenesis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays, single lab","pmids":["22851688"],"is_preprint":false}],"current_model":"EIF5 is a bifunctional regulator of eukaryotic translation initiation: its N-terminal domain contains an arginine-finger GAP that stimulates GTP hydrolysis by eIF2 upon AUG start-codon recognition (displacing eIF1 from the 40S PIC and stabilizing the closed, tRNA-accommodated state), while its C-terminal HEAT/W2 domain serves as a scaffold that simultaneously contacts eIF2β, eIF3c/NIP1, eIF1, eIF4G, and eIF5B to nucleate and remodel the multifactor preinitiation complex; additionally, eIF5 acts as a GDP dissociation inhibitor (GDI) for eIF2•GDP between initiation rounds, a function antagonized by eIF2B (GDF/GEF) and modulated by CK2 phosphorylation of eIF5."},"narrative":{"mechanistic_narrative":"eIF5 is a bifunctional regulator of eukaryotic translation initiation that couples GTP hydrolysis on eIF2 to AUG start-codon recognition and the assembly of the multifactor preinitiation complex [PMID:8161539, PMID:11166181]. It functions as a GTPase-activating protein (GAP) for eIF2: forming a 1:1 complex with eIF2, its N-terminal domain supplies an 'arginine finger' (Arg15, with a contribution from Arg48) that stimulates hydrolysis of eIF2-bound GTP in the 40S initiation complex, an activity required for 80S complex formation and translation [PMID:8161539, PMID:11166181]. Through a glutamic acid-rich bipartite motif in its α-helical, HEAT/W2-type C-terminal domain (CTD), eIF5 bridges eIF2 (via eIF2β) and eIF3 (via the NIP1/eIF3c N-terminus) and simultaneously contacts eIF1, eIF4G, and eIF5B, nucleating the multifactor complex (MFC) that also contains initiator tRNA(Met); disruption of this motif (tif5-7A) collapses MFC assembly and impairs initiation [PMID:11018020, PMID:10805737, PMID:16781736]. eIF5 enforces start-codon fidelity by controlling Pi release and the open-to-closed conformational transition of the scanning PIC: its CTD antagonizes eIF1 binding, eIF1 dissociation coupled to eIF1A-CTT movement toward the eIF5-NTD triggers Pi release, and the eIF5-NTD engages Met-tRNAi at the position vacated by eIF1 to stabilize the accommodated state [PMID:23293029, PMID:25114053, PMID:30475211]. Beyond the GAP cycle, eIF5 acts as a GDP dissociation inhibitor (GDI) that stabilizes eIF2•GDP between initiation rounds — a distinct activity that requires eIF2β and is displaced by eIF2B acting as a GDP dissociation factor (GDF) prior to nucleotide exchange [PMID:20485439, PMID:24352424, PMID:27458202]. eIF5 is phosphorylated by casein kinase II within a C-terminal acidic cluster (Ser-387/Ser-388), which increases its affinity for eIF2β, eIF1A, and other CTD partners [PMID:11861906, PMID:34923394, PMID:40670154]. eIF5 GAP activity preferentially stimulates poly-GA RAN translation from a CUG near-cognate codon in C9orf72 FTLD/ALS, linking the factor to repeat-associated non-AUG translation [PMID:38301895].","teleology":[{"year":1994,"claim":"Established that eIF5 directly partners eIF2 and that this complex is the unit responsible for hydrolyzing GTP at the 40S initiation complex, defining eIF5's core catalytic role.","evidence":"Glycerol gradient sedimentation and in vitro GTPase/80S assembly assays with purified recombinant eIF5","pmids":["8161539"],"confidence":"High","gaps":["Did not identify the catalytic residue or mechanism of GAP action","Stoichiometry within the larger 40S complex not resolved"]},{"year":2000,"claim":"Defined eIF5 as the physical scaffold of the multifactor complex, showing its glutamic acid-rich bipartite CTD motif bridges eIF2β and eIF3c to assemble eIF1 and initiator tRNA into one entity.","evidence":"In vitro binding, co-IP from yeast extracts, and the tif5-7A bipartite-motif mutant; alanine substitution of conserved glutamates","pmids":["11018020","10805737","9671501"],"confidence":"High","gaps":["Atomic basis of the bipartite interactions not yet resolved","How MFC assembly couples to ribosome loading unclear"]},{"year":2001,"claim":"Identified eIF5 as a classical arginine-finger GAP for eIF2 and showed it bridges the cap-binding eIF4G to the PIC, placing 48S-to-80S conversion as the rate-limiting initiation step.","evidence":"AlF4- transition-state mimic binding, R15M/R48M mutagenesis with GTPase and in vitro translation readouts; GST pulldowns and polysome analysis","pmids":["11166181","11331597"],"confidence":"High","gaps":["Structure of the catalytic NTD on the ribosome not yet available","How GAP triggering is timed to AUG recognition not yet defined"]},{"year":2004,"claim":"Showed that the eIF3c/NIP1 N-terminal domain coordinates eIF1–eIF5 contacts to suppress GTP hydrolysis at non-AUG codons, linking MFC architecture to start-codon fidelity.","evidence":"NIP1-NTD mutagenesis, yeast Sui- genetics, in vitro binding, and eIF1/eIF5 overexpression suppression","pmids":["15485912"],"confidence":"High","gaps":["Molecular switch converting fidelity-checkpoint to GAP-active state not defined","Quantitative contribution of each contact to AUG selection unclear"]},{"year":2006,"claim":"Provided atomic structures of the eIF5-CTD (human and yeast), revealing an α-helical HEAT/W2 domain homologous to eIF2Bε-CTD and mapping non-overlapping electrostatic patches for eIF2β and eIF3c.","evidence":"X-ray crystallography of human (high-resolution) and S. cerevisiae (1.5 Å) eIF5-CTD with electrostatic surface analysis","pmids":["16781736","16616930"],"confidence":"High","gaps":["Did not capture partner-bound complexes","Conformation of the catalytic NTD unresolved"]},{"year":2010,"claim":"Revealed a second, GAP-independent function for eIF5 as a GDP dissociation inhibitor that retains eIF2•GDP between rounds and as a component of the eIF2(αP) complex inhibiting eIF2B, mechanistically separating fidelity from recycling control.","evidence":"Fluorescence nucleotide-binding assays, GDI-specific residue mutagenesis, GCN4 genetic assays, in vitro GEF inhibition","pmids":["20485439"],"confidence":"High","gaps":["Structural basis of GDI clamping on eIF2•GDP not resolved","How the GAP-to-GDI handoff is regulated unclear"]},{"year":2013,"claim":"Defined how eIF5-bound eIF2•GDP is recycled, identifying eIF2B as a GDF that displaces eIF5 GDI before exchanging nucleotide, with GDF and GEF being independent and differently regulated by eIF2α phosphorylation.","evidence":"Protein-interaction and fluorescent nucleotide-exchange kinetic assays with eIF2B subunit mutagenesis","pmids":["24352424"],"confidence":"High","gaps":["Structural mechanism of GDI displacement not resolved","In vivo flux through the GDF step not quantified"]},{"year":2013,"claim":"Resolved the conformational trigger for hydrolysis completion, showing eIF1A-CTT movement toward the eIF5-NTD coupled to eIF1 dissociation drives Pi release, with the eIF5-CTD antagonizing eIF1.","evidence":"FRET distance measurements in reconstituted yeast PICs, mutagenesis, and phosphate release assays","pmids":["23293029"],"confidence":"High","gaps":["Order of eIF1 release versus eIF1A movement not fully resolved","Structural snapshot of the transition state lacking"]},{"year":2014,"claim":"Demonstrated that eIF5 controls both Pi release and the open-to-closed PIC transition, with the Sui- G31R mutation stabilizing the closed state at UUG, mechanistically linking eIF5 to start-codon accuracy.","evidence":"In vitro GTP hydrolysis, Pi release, and FRET PIC-conformation assays with systematic eIF5 mutagenesis; reconstituted 48S assembly with eIF5B","pmids":["25114053","25260592"],"confidence":"High","gaps":["How eIF5 distinguishes cognate from near-cognate codons mechanistically incomplete","Handoff from eIF5 to eIF5B in subunit joining not structurally defined"]},{"year":2018,"claim":"Captured the eIF5-NTD on the 40S subunit at the site vacated by eIF1, showing it engages Met-tRNAi to favor the accommodated PIN state, providing a structural basis for fidelity control.","evidence":"3.0 Å cryo-EM of a yeast 48S PIC with in vivo UUG assays and in vitro conformation assays","pmids":["30475211"],"confidence":"High","gaps":["Pre-hydrolysis catalytic geometry of the arginine finger not captured","Dynamics of NTD docking after eIF1 release not time-resolved"]},{"year":2018,"claim":"Showed human eIF5 binds eIF5B via a C-terminal motif with much higher affinity than eIF1A, suggesting eIF5 coordinates start-codon selection with subunit joining and is displaced by eIF1A to leave the ribosome.","evidence":"ITC/fluorescence binding affinity and competition assays with eIF5B-binding motif identification","pmids":["30211544"],"confidence":"Medium","gaps":["Single lab; reciprocal in vivo validation lacking","Structural detail of the eIF5–eIF5B interface not resolved"]},{"year":2021,"claim":"Defined eIF5's intrinsically disordered DWEAR and CTT regions as competing intramolecular elements that toggle CTD preference between eIF2β and eIF1A, and showed CK2 phosphorylation increases eIF2 affinity.","evidence":"NMR spectroscopy, binding assays, and phosphomimetic mutagenesis of human eIF5","pmids":["34923394"],"confidence":"Medium","gaps":["Single lab; functional consequence of IDR toggling in vivo not tested","Number of eIF2β binding sites not definitively established"]},{"year":2024,"claim":"Linked eIF5 GAP activity to disease by showing it preferentially stimulates poly-GA RAN translation from a CUG near-cognate codon in C9orf72 FTLD/ALS, with catalytic activity required.","evidence":"WT versus inactive eIF5 mutant transfection, RAN reporters, codon mutagenesis, and Drosophila RNAi knockdown","pmids":["38301895"],"confidence":"Medium","gaps":["Single lab; 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cells","date":"2025-02-10","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.10.636994","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":29185,"output_tokens":7154,"usd":0.097433,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16333,"output_tokens":4965,"usd":0.102895,"stage2_stop_reason":"end_turn"},"total_usd":0.200328,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1994,\n      \"finding\": \"eIF5 forms a specific complex with eIF2 in a 1:1 stoichiometry (apparent Mr ~160 kDa), and this interaction is required for eIF5 to catalyze hydrolysis of GTP bound to the 40S initiation complex and promote 80S initiation complex formation.\",\n      \"method\": \"Glycerol gradient sedimentation, in vitro GTPase assay with purified recombinant eIF5\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified proteins, replicated in multiple subsequent studies\",\n      \"pmids\": [\"8161539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"eIF5 stably associates with the yeast eIF3 core complex (composed of Tif32p/eIF3a, Nip1p/eIF3c, Prt1p/eIF3b, Tif34p/eIF3i, Tif35p/eIF3g); Nip1p/eIF3c directly binds eIF5 in two-hybrid and in vitro binding assays.\",\n      \"method\": \"Ni2+ affinity purification of His-Prt1p complex, mass spectrometry, yeast two-hybrid, in vitro protein binding\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (affinity purification, MS, two-hybrid, in vitro binding), replicated in subsequent studies\",\n      \"pmids\": [\"9671501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"eIF5 bridges interaction between eIF3 (via NIP1/eIF3c N-terminus) and eIF2 (via eIF2β N-terminal half) through a conserved bipartite motif in the eIF5 C-terminal domain (CTD), forming a multifactor complex (MFC) that also contains eIF1 and initiator tRNA(Met) in vivo. The tif5-7A mutation in the bipartite motif disrupts MFC assembly and causes temperature-sensitive growth and reduction in translation initiation.\",\n      \"method\": \"In vitro protein binding, co-immunoprecipitation from yeast cell extracts, genetic analysis (tif5-7A mutant)\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays plus in vivo MFC disruption phenotype, replicated across labs\",\n      \"pmids\": [\"11018020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The C-terminus of eIF5 (glutamic acid-rich bipartite motif) is required for interaction with the β subunit of eIF2; alanine substitution of conserved glutamic acid residues (E346A/E347A and E384A/E385A) abolishes eIF5–eIF2β binding, GTP hydrolysis, 80S initiation complex formation, and in vivo cell viability.\",\n      \"method\": \"Deletion and alanine substitution mutagenesis, in vitro binding assays, GTPase assay, yeast complementation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis with multiple orthogonal functional assays (binding, GTPase, 80S formation, in vivo rescue)\",\n      \"pmids\": [\"10805737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"eIF5 acts as a classical GTPase-activating protein (GAP) for eIF2: its interaction with eIF2 is enhanced by AlF4- (mimicking the transition state), and it contains an 'arginine finger' (Arg15) flanked by hydrophobic residues; mutation R15M abolishes both GTP hydrolysis stimulation and in vitro mRNA translation. Arg48 also contributes to the GTPase active site.\",\n      \"method\": \"AlF4- binding assay, site-directed mutagenesis (R15M, R48M), in vitro GTPase assay, in vitro translation assay\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of catalytic residues with multiple functional readouts, replicated mechanistically\",\n      \"pmids\": [\"11166181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The eIF5-CTD simultaneously binds eIF4G (cap-binding complex subunit) and eIF3/NIP1, suggesting it bridges the cap-binding complex to the PIC. In vivo, the tif5-7A mutation (disrupting MFC) eliminates eIF5 from the pre-initiation complex and causes accumulation of 48S complexes, indicating GTP hydrolysis/conversion of 48S to 80S is the rate-limiting step.\",\n      \"method\": \"In vitro protein binding, GST pulldown, polysome/ribosome sedimentation analysis, in vivo crosslinking\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (pulldown, sedimentation, in vivo), consistent with prior findings\",\n      \"pmids\": [\"11331597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"eIF5 makes critical contacts with the 40S ribosomal subunit in vivo, performing redundant functions with the TIF32-CTD of eIF3a for 40S binding. The TIF32-CTD binds helices 16–18 of 18S rRNA in vitro, and NIP1/eIF5 interact with 40S protein RPS0A.\",\n      \"method\": \"In vivo co-immunoprecipitation from yeast, in vitro RNA binding assay, deletion analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two methods (in vivo IP, in vitro binding), single lab\",\n      \"pmids\": [\"12651896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The eIF4G HEAT domain interacts with eIF5 (and eIF1); eIF1 binds simultaneously to eIF4G and eIF3c in vitro; mutations disrupting eIF4G–eIF5 interaction lead to elevated non-AUG initiation in vivo, indicating the eIF4G HEAT domain–eIF5/eIF1 interaction is important for scanning preinitiation complex integrity and AUG stringency.\",\n      \"method\": \"In vitro protein binding, two-hybrid, in vivo genetic suppression, reporter assay for non-AUG initiation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods, single lab\",\n      \"pmids\": [\"12861028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The N-terminal domain (NTD) of NIP1/eIF3c directly binds eIF1 and eIF5 to form the MFC; specific NIP1-NTD mutations reduce eIF1 or eIF5 binding, alter UUG start codon utilization (Sui- phenotype), and impair TC recruitment to 40S ribosomes. eIF1 overexpression suppresses the Sui- phenotype of both NIP1 and eIF5-G31R mutants, indicating that NIP1-NTD coordinates eIF1–eIF5 interaction to inhibit GTP hydrolysis at non-AUG codons.\",\n      \"method\": \"Site-directed mutagenesis of NIP1-NTD, yeast genetics (Sui- phenotype assay), in vitro binding, eIF1/eIF5 overexpression suppression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (mutagenesis, genetics, binding assays), consistent mechanistic model\",\n      \"pmids\": [\"15485912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structure of the human eIF5-CTD at high resolution shows it is exclusively α-helical and homologous to the eIF2Bε-CTD (W2/HEAT domain). The binding sites for eIF2β, eIF3c, and eIF1 were mapped onto the structure: eIF2β and eIF3c bind non-overlapping patches of negative and positive electrostatic potential, respectively.\",\n      \"method\": \"X-ray crystallography (crystal structure), electrostatic surface analysis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution crystal structure with functional site mapping, independently confirmed by S. cerevisiae structure\",\n      \"pmids\": [\"16781736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structure of the S. cerevisiae eIF5-CTD at 1.5 Å confirms it contains an atypical HEAT motif; surface analysis identifies conserved potential interaction regions for partner eIFs.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure at 1.5 Å resolution, consistent with human eIF5-CTD structure\",\n      \"pmids\": [\"16616930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"eIF1 has two distinct eIF5-binding faces: its N-terminal tail and a basic/hydrophobic surface (KH region). Mutation of the KH region is lethal and causes dominant relaxation of start codon selection. The eIF1 N-terminal tail plays a stimulatory role in cooperative MFC assembly.\",\n      \"method\": \"NMR solution structure of yeast eIF1 used for interface mapping, yeast two-hybrid, in vitro binding, genetic analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR-guided mutagenesis with in vitro and in vivo functional validation\",\n      \"pmids\": [\"17974565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"eIF5 has a GDP dissociation inhibitor (GDI) activity distinct from its GAP function: it stabilizes GDP binding to eIF2 between rounds of initiation. Conserved residues in eIF5 are required specifically for GDI (not GAP) activity. eIF5 is also a critical component of the eIF2(αP) regulatory complex that inhibits eIF2B GEF activity.\",\n      \"method\": \"Fluorescence nucleotide binding assays, mutagenesis of eIF5 GDI-specific residues, genetic assays (GCN4 translational control), in vitro GEF inhibition assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal in vitro assays plus genetic validation, published in Nature\",\n      \"pmids\": [\"20485439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"eIF2B acts as a GDI displacement factor (GDF) that recruits eIF2 from the eIF2•GDP/eIF5 GDI complex prior to GEF action; GDF activity depends on eIF2Bε and eIF2Bγ subunits and is insensitive to eIF2α phosphorylation (unlike GEF). eIF2B GDF and GEF activities are independent.\",\n      \"method\": \"Protein-protein interaction assays, fluorescent nucleotide exchange kinetic assays, mutagenesis of eIF2B subunits\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — kinetic assays with purified factors, mutagenesis separating GDF from GEF function\",\n      \"pmids\": [\"24352424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Upon AUG codon recognition, the C-terminal tail (CTT) of eIF1A moves closer to the eIF5 NTD; this movement is coupled to eIF1 dissociation from the PIC. eIF1 dissociation plus eIF1A-CTT movement toward eIF5 is required to trigger Pi release from eIF2•GDP•Pi. The eIF5-CTD antagonizes eIF1 binding to the PIC.\",\n      \"method\": \"FRET-based distance measurements in reconstituted yeast PICs, mutagenesis, phosphate release assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — FRET in reconstituted system plus mutagenesis and phosphate release assays\",\n      \"pmids\": [\"23293029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"eIF5-G31R (Sui- mutation) alters Pi release: it accelerates Pi release at UUG codons and decreases it at AUG codons, stabilizing the closed PIC conformation at UUG. Suppressor G62S mitigates both defects; suppressor M18V primarily impairs GTP hydrolysis with little effect on PIC conformation, indicating eIF5 controls both Pi release and open-to-closed PIC conformational transitions for accurate AUG selection.\",\n      \"method\": \"In vitro GTP hydrolysis assays, Pi release assays, FRET-based PIC conformation assays, mutagenesis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple in vitro functional assays with systematic mutagenesis\",\n      \"pmids\": [\"25114053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"eIF5 and eIF5B together stimulate 48S initiation complex formation during ribosomal scanning; eIF5-induced hydrolysis of eIF2-bound GTP is essential for this stimulation, increasing the probability that scanning complexes arrest at non-optimal start codons. eIF5B then stabilizes the initiator tRNA in the P site after eIF2•GDP dissociation.\",\n      \"method\": \"In vitro 48S IC assembly assays, GTPase assays, mutagenesis of eIF1A and eIF5B\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro system with mutagenesis and multiple readouts\",\n      \"pmids\": [\"25260592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Casein kinase II (CK II) phosphorylates mammalian eIF5 in vitro and in vivo at Ser-387 and Ser-388 near the C-terminus (within an acidic cluster), accounting for ~90% of total phosphorylation; a minor site is Ser-174. Alanine substitution at S387/S388 abolishes both in vitro and in vivo phosphorylation.\",\n      \"method\": \"Kinase isolation and biochemical characterization, mass spectrometry of phosphorylation sites, alanine substitution mutagenesis, in vivo 32P labeling\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — MS site mapping combined with mutagenesis and in vivo labeling\",\n      \"pmids\": [\"11861906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In S. cerevisiae, eIF5 is phosphorylated in vivo on multiple serine residues by casein kinase II; phosphopeptide mapping reveals four major sites identical to in vitro CK II sites. However, Ser-to-Ala mutations at all five CK II consensus sites in eIF5 had no obvious effect on cell growth under normal conditions.\",\n      \"method\": \"In vivo 32P labeling and phosphopeptide mapping, conditional CK II mutant yeast strain, site-directed mutagenesis\",\n      \"journal\": \"Yeast\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo phosphorylation confirmed by multiple methods; functional significance unclear (negative growth result under normal conditions)\",\n      \"pmids\": [\"12518314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The eIF3c N-terminal domain (NTD) is divided into 3c0, 3c1, and 3c2 sub-regions; 3c0 binds eIF5 strongly but only weakly to eIF1's ribosome-binding surface, while 3c1/3c2 form a stoichiometric complex with eIF1. The 3c0:eIF5 interaction stabilizes the scanning PIC by preventing the inhibitory 3c0:eIF1 interaction; upon start codon recognition, interactions involving eIF5 and ultimately 3c0:eIF1 facilitate eIF1 release.\",\n      \"method\": \"NMR, in vitro binding assays, mutagenesis of NIP1-NTD subregions\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural data combined with mutagenesis and binding assays\",\n      \"pmids\": [\"28297669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Cryo-EM structure (3.0 Å) of a yeast 48S PIC shows the eIF5-NTD bound to the 40S subunit at the location vacated by eIF1; eIF5-NTD interacts with Met-tRNAi to allow a more accommodated (PIN) orientation. Substitutions of eIF5 residues at the eIF5-NTD/tRNAi interface influence initiation at near-cognate UUG codons in vivo and closed/open PIC conformation in vitro.\",\n      \"method\": \"Cryo-EM reconstruction, in vivo UUG initiation assays, in vitro PIC conformation assays, mutagenesis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with mutagenesis and orthogonal functional assays\",\n      \"pmids\": [\"30475211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Human eIF5 interacts with eIF5B via a C-terminal eIF5B-binding motif, competing with eIF1A for eIF5B binding with ~100-fold higher affinity than eIF1A; this interaction may coordinate start codon selection (eIF5 as GAP of eIF2) with ribosomal subunit joining (eIF5B), with eIF1A displacing eIF5 from eIF5B to allow the eIF5:eIF2-GDP complex to leave the ribosome.\",\n      \"method\": \"Binding affinity measurements (ITC/fluorescence), competition assays, identification of eIF5B-binding motif in eIF5\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative binding assays with motif identification, single lab\",\n      \"pmids\": [\"30211544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"eIF2β acts in concert with eIF5 to prevent premature GDP release from eIF2γ: a growth suppressor mutation in eIF2β specifically prevents eIF5 GDI from stabilizing GDP binding to eIF2 (increases GDP off-rate from eIF2•GDP/eIF5 complexes) without affecting intrinsic eIF2 affinities for GDP or initiator tRNA, impairing GCN4 translational control.\",\n      \"method\": \"Fluorescent nucleotide binding kinetics assays, genetic analysis (GCN4 derepression), mutagenesis of eIF2β\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — kinetic assays with purified factors plus genetic validation; delineates GDI mechanism\",\n      \"pmids\": [\"27458202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Human eIF5 contains two intrinsically disordered regions (IDRs): the DWEAR motif and the C-terminal tail (CTT), which dynamically contact the folded CTD and compete with each other. CTD•CTT interaction favors eIF2β binding to eIF5-CTD, whereas CTD•DWEAR interaction favors eIF1A binding. CK2 phosphorylation significantly increases eIF5 affinity for eIF2; eIF2β has at least two (likely three) eIF5-binding sites.\",\n      \"method\": \"NMR spectroscopy, binding assays, phosphomimetic mutagenesis\",\n      \"journal\": \"Biophysical chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR plus binding assays, single lab\",\n      \"pmids\": [\"34923394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CK2 phosphorylation of eIF5 increases its affinity for eIF1A; a new contact interface was identified between eIF5-CTD and the OB domain of eIF1A. Dynamic intramolecular interactions within both eIF5 and eIF1A modulate this interaction.\",\n      \"method\": \"Binding assays, phosphomimetic mutagenesis of eIF5, NMR/structural analysis\",\n      \"journal\": \"Current research in structural biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — binding assays with mutagenesis, single lab; extends prior IDR findings\",\n      \"pmids\": [\"36164648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"eIF5 (via its GAP activity) preferentially stimulates poly-GA RAN translation from a CUG near-cognate start codon in C9orf72 FTLD/ALS; inactive eIF5 mutants do not stimulate. Mutation of the CUG to CCG or AUG abolishes the stimulatory effect. In a Drosophila C9orf72 model, knockdown of eIF5 reduces poly-GA expression in vivo.\",\n      \"method\": \"Transfection of WT and inactive eIF5 mutants, RAN translation reporters, codon mutation analysis, Drosophila RNAi knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (cell-based reporters, mutagenesis, in vivo Drosophila), single lab\",\n      \"pmids\": [\"38301895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Single-molecule fluorescence analysis of human translation initiation showed that eIF5 only transiently binds initiation complexes late in initiation immediately prior to eIF5B association; eIF5 association requires a translation start site and is inhibited by alternative start sites. eIF1 and eIF5 have opposing roles during initiation (knockdown/overexpression experiments in human cells confirmed this).\",\n      \"method\": \"Single-molecule fluorescence (smFRET/TIRF) on reconstituted human PICs, knockdown and overexpression in human cells\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule reconstitution plus cell validation; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"39026837\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Crystal structure of yeast eIF5-CTD in complex with eIF2β K-box 3 reveals an extended binding site on eIF2β beyond the K-box. eIF2β has three distinct binding sites (one per K-box), and human eIF5, eIF2Bε, and 5MP1 can all bind to all three sites while reducing each other's affinities. CK2 phosphomimetic mutations in eIF5 increase affinities for all these partners, and eIF2B speeds dissociation of eIF5 from eIF2-GDP to promote nucleotide exchange.\",\n      \"method\": \"X-ray crystallography, NMR, binding assays with phosphomimetic mutants\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with NMR and quantitative binding assays, multiple orthogonal methods\",\n      \"pmids\": [\"40670154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Sequential binding of eIF5-CTD to the eIF4G RS1 domain and eIF2β K-boxes stabilizes the 48S PIC and promotes its shift to initiation mode: eIF4G-RS1/eIF5-CTD interaction directly links eIF4G to the PIC to enhance mRNA binding; eIF2β-K-boxes increase mRNA binding in a manner reversed by eIF5-CTD; mutations in these interactions restore AUG selection accuracy impaired by an eIF2β mutation.\",\n      \"method\": \"In vitro 48S complex assembly, mRNA binding assays, in vivo start codon selection assays, mutagenesis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays, single lab\",\n      \"pmids\": [\"22851688\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EIF5 is a bifunctional regulator of eukaryotic translation initiation: its N-terminal domain contains an arginine-finger GAP that stimulates GTP hydrolysis by eIF2 upon AUG start-codon recognition (displacing eIF1 from the 40S PIC and stabilizing the closed, tRNA-accommodated state), while its C-terminal HEAT/W2 domain serves as a scaffold that simultaneously contacts eIF2β, eIF3c/NIP1, eIF1, eIF4G, and eIF5B to nucleate and remodel the multifactor preinitiation complex; additionally, eIF5 acts as a GDP dissociation inhibitor (GDI) for eIF2•GDP between initiation rounds, a function antagonized by eIF2B (GDF/GEF) and modulated by CK2 phosphorylation of eIF5.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"eIF5 is a bifunctional regulator of eukaryotic translation initiation that couples GTP hydrolysis on eIF2 to AUG start-codon recognition and the assembly of the multifactor preinitiation complex [#0, #4]. It functions as a GTPase-activating protein (GAP) for eIF2: forming a 1:1 complex with eIF2, its N-terminal domain supplies an 'arginine finger' (Arg15, with a contribution from Arg48) that stimulates hydrolysis of eIF2-bound GTP in the 40S initiation complex, an activity required for 80S complex formation and translation [#0, #4]. Through a glutamic acid-rich bipartite motif in its α-helical, HEAT/W2-type C-terminal domain (CTD), eIF5 bridges eIF2 (via eIF2β) and eIF3 (via the NIP1/eIF3c N-terminus) and simultaneously contacts eIF1, eIF4G, and eIF5B, nucleating the multifactor complex (MFC) that also contains initiator tRNA(Met); disruption of this motif (tif5-7A) collapses MFC assembly and impairs initiation [#2, #3, #9]. eIF5 enforces start-codon fidelity by controlling Pi release and the open-to-closed conformational transition of the scanning PIC: its CTD antagonizes eIF1 binding, eIF1 dissociation coupled to eIF1A-CTT movement toward the eIF5-NTD triggers Pi release, and the eIF5-NTD engages Met-tRNAi at the position vacated by eIF1 to stabilize the accommodated state [#14, #15, #20]. Beyond the GAP cycle, eIF5 acts as a GDP dissociation inhibitor (GDI) that stabilizes eIF2•GDP between initiation rounds — a distinct activity that requires eIF2β and is displaced by eIF2B acting as a GDP dissociation factor (GDF) prior to nucleotide exchange [#12, #13, #22]. eIF5 is phosphorylated by casein kinase II within a C-terminal acidic cluster (Ser-387/Ser-388), which increases its affinity for eIF2β, eIF1A, and other CTD partners [#17, #23, #27]. eIF5 GAP activity preferentially stimulates poly-GA RAN translation from a CUG near-cognate codon in C9orf72 FTLD/ALS, linking the factor to repeat-associated non-AUG translation [#25].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established that eIF5 directly partners eIF2 and that this complex is the unit responsible for hydrolyzing GTP at the 40S initiation complex, defining eIF5's core catalytic role.\",\n      \"evidence\": \"Glycerol gradient sedimentation and in vitro GTPase/80S assembly assays with purified recombinant eIF5\",\n      \"pmids\": [\"8161539\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the catalytic residue or mechanism of GAP action\", \"Stoichiometry within the larger 40S complex not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined eIF5 as the physical scaffold of the multifactor complex, showing its glutamic acid-rich bipartite CTD motif bridges eIF2β and eIF3c to assemble eIF1 and initiator tRNA into one entity.\",\n      \"evidence\": \"In vitro binding, co-IP from yeast extracts, and the tif5-7A bipartite-motif mutant; alanine substitution of conserved glutamates\",\n      \"pmids\": [\"11018020\", \"10805737\", \"9671501\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic basis of the bipartite interactions not yet resolved\", \"How MFC assembly couples to ribosome loading unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified eIF5 as a classical arginine-finger GAP for eIF2 and showed it bridges the cap-binding eIF4G to the PIC, placing 48S-to-80S conversion as the rate-limiting initiation step.\",\n      \"evidence\": \"AlF4- transition-state mimic binding, R15M/R48M mutagenesis with GTPase and in vitro translation readouts; GST pulldowns and polysome analysis\",\n      \"pmids\": [\"11166181\", \"11331597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the catalytic NTD on the ribosome not yet available\", \"How GAP triggering is timed to AUG recognition not yet defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed that the eIF3c/NIP1 N-terminal domain coordinates eIF1–eIF5 contacts to suppress GTP hydrolysis at non-AUG codons, linking MFC architecture to start-codon fidelity.\",\n      \"evidence\": \"NIP1-NTD mutagenesis, yeast Sui- genetics, in vitro binding, and eIF1/eIF5 overexpression suppression\",\n      \"pmids\": [\"15485912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular switch converting fidelity-checkpoint to GAP-active state not defined\", \"Quantitative contribution of each contact to AUG selection unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided atomic structures of the eIF5-CTD (human and yeast), revealing an α-helical HEAT/W2 domain homologous to eIF2Bε-CTD and mapping non-overlapping electrostatic patches for eIF2β and eIF3c.\",\n      \"evidence\": \"X-ray crystallography of human (high-resolution) and S. cerevisiae (1.5 Å) eIF5-CTD with electrostatic surface analysis\",\n      \"pmids\": [\"16781736\", \"16616930\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not capture partner-bound complexes\", \"Conformation of the catalytic NTD unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealed a second, GAP-independent function for eIF5 as a GDP dissociation inhibitor that retains eIF2•GDP between rounds and as a component of the eIF2(αP) complex inhibiting eIF2B, mechanistically separating fidelity from recycling control.\",\n      \"evidence\": \"Fluorescence nucleotide-binding assays, GDI-specific residue mutagenesis, GCN4 genetic assays, in vitro GEF inhibition\",\n      \"pmids\": [\"20485439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of GDI clamping on eIF2•GDP not resolved\", \"How the GAP-to-GDI handoff is regulated unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined how eIF5-bound eIF2•GDP is recycled, identifying eIF2B as a GDF that displaces eIF5 GDI before exchanging nucleotide, with GDF and GEF being independent and differently regulated by eIF2α phosphorylation.\",\n      \"evidence\": \"Protein-interaction and fluorescent nucleotide-exchange kinetic assays with eIF2B subunit mutagenesis\",\n      \"pmids\": [\"24352424\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of GDI displacement not resolved\", \"In vivo flux through the GDF step not quantified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved the conformational trigger for hydrolysis completion, showing eIF1A-CTT movement toward the eIF5-NTD coupled to eIF1 dissociation drives Pi release, with the eIF5-CTD antagonizing eIF1.\",\n      \"evidence\": \"FRET distance measurements in reconstituted yeast PICs, mutagenesis, and phosphate release assays\",\n      \"pmids\": [\"23293029\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of eIF1 release versus eIF1A movement not fully resolved\", \"Structural snapshot of the transition state lacking\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated that eIF5 controls both Pi release and the open-to-closed PIC transition, with the Sui- G31R mutation stabilizing the closed state at UUG, mechanistically linking eIF5 to start-codon accuracy.\",\n      \"evidence\": \"In vitro GTP hydrolysis, Pi release, and FRET PIC-conformation assays with systematic eIF5 mutagenesis; reconstituted 48S assembly with eIF5B\",\n      \"pmids\": [\"25114053\", \"25260592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How eIF5 distinguishes cognate from near-cognate codons mechanistically incomplete\", \"Handoff from eIF5 to eIF5B in subunit joining not structurally defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Captured the eIF5-NTD on the 40S subunit at the site vacated by eIF1, showing it engages Met-tRNAi to favor the accommodated PIN state, providing a structural basis for fidelity control.\",\n      \"evidence\": \"3.0 Å cryo-EM of a yeast 48S PIC with in vivo UUG assays and in vitro conformation assays\",\n      \"pmids\": [\"30475211\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Pre-hydrolysis catalytic geometry of the arginine finger not captured\", \"Dynamics of NTD docking after eIF1 release not time-resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed human eIF5 binds eIF5B via a C-terminal motif with much higher affinity than eIF1A, suggesting eIF5 coordinates start-codon selection with subunit joining and is displaced by eIF1A to leave the ribosome.\",\n      \"evidence\": \"ITC/fluorescence binding affinity and competition assays with eIF5B-binding motif identification\",\n      \"pmids\": [\"30211544\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; reciprocal in vivo validation lacking\", \"Structural detail of the eIF5–eIF5B interface not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined eIF5's intrinsically disordered DWEAR and CTT regions as competing intramolecular elements that toggle CTD preference between eIF2β and eIF1A, and showed CK2 phosphorylation increases eIF2 affinity.\",\n      \"evidence\": \"NMR spectroscopy, binding assays, and phosphomimetic mutagenesis of human eIF5\",\n      \"pmids\": [\"34923394\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; functional consequence of IDR toggling in vivo not tested\", \"Number of eIF2β binding sites not definitively established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked eIF5 GAP activity to disease by showing it preferentially stimulates poly-GA RAN translation from a CUG near-cognate codon in C9orf72 FTLD/ALS, with catalytic activity required.\",\n      \"evidence\": \"WT versus inactive eIF5 mutant transfection, RAN reporters, codon mutagenesis, and Drosophila RNAi knockdown\",\n      \"pmids\": [\"38301895\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; mechanism of CUG preference at the molecular level unclear\", \"Therapeutic relevance of eIF5 targeting untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided a co-crystal structure of yeast eIF5-CTD bound to eIF2β K-box 3 and showed three competing K-box sites shared by eIF5, eIF2Bε and 5MP1, with CK2 phosphomimetics raising all partner affinities and eIF2B accelerating eIF5 release for exchange.\",\n      \"evidence\": \"X-ray crystallography, NMR, and quantitative binding assays with phosphomimetic mutants\",\n      \"pmids\": [\"40670154\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo competition among eIF5/eIF2Bε/5MP1 not quantified\", \"How phosphorylation-tuned affinities are coordinated through the cycle unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How eIF5's transient, late association with the initiation complex and its dual GAP/GDI roles are dynamically choreographed and regulated in human cells remains incompletely defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Time-resolved structural states of the catalytic NTD across the hydrolysis cycle lacking\", \"Physiological regulation of CK2-dependent affinity tuning not established\", \"Integration of GAP, GDI and eIF5B-handoff roles in vivo not unified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 4, 12]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 5, 9]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [12, 13, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005840\", \"supporting_discovery_ids\": [6, 20]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-72613\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 4, 16]}\n    ],\n    \"complexes\": [\"eIF2-eIF5 complex\", \"multifactor complex (MFC)\", \"eIF3 core complex\", \"eIF2(αP) regulatory complex\"],\n    \"partners\": [\"EIF2S2\", \"EIF3C\", \"EIF1\", \"EIF4G\", \"EIF5B\", \"EIF1AX\", \"EIF2B5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}