{"gene":"LTV1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2006,"finding":"Ltv1 shuttles between nucleus and cytoplasm in a Crm1-dependent manner and contains a functional nuclear export sequence (NES) sufficient to direct export of an NLS-containing reporter. Ltv1 co-sediments with 43S/40S subunits and copurifies with late 43S particles. Loss of LTV1 reduces small subunit export as judged by altered distribution of 5'-ITS1 rRNA and RpS3. Genetic interaction was identified between LTV1 and YRB2 (a Ran-GTP/Crm1-binding protein), placing Ltv1 as an adapter linking nuclear export machinery to the small subunit.","method":"Sucrose gradient co-sedimentation, copurification, shuttling assay (heterokaryon/reporter), FISH/fluorescence localization, genetic interaction analysis","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biochemical co-sedimentation, export reporter assay, localization, genetic epistasis) replicated across multiple experiments in one study, with additional genetic corroboration","pmids":["16888326"],"is_preprint":false},{"year":2004,"finding":"Ltv1 physically interacts with Yar1 (an ankyrin-repeat protein) and RpS3 as part of a pre-40S complex. Loss of LTV1 results in reduced absolute numbers of 40S subunits and excess free 60S subunits, indicating a role in 40S subunit production. Overexpression of RPS3 does not suppress the ribosome biogenesis defect of Δltv1, distinguishing Ltv1's role from that of Yar1.","method":"Co-immunoprecipitation, polysome profiling, genetic suppression analysis","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal genetic and biochemical interactions shown, single lab, multiple orthogonal methods","pmids":["15611164"],"is_preprint":false},{"year":2010,"finding":"Mutation or deletion of the putative NES in Ltv1 is strongly dominant negative; the dominant-negative mutant protein accumulates in the cytoplasm associated with pre-40S subunits, causes accumulation of 20S rRNA in the cytoplasm (detected by FISH), retains late biogenesis factor Tsr1 in the cytoplasm, and leads to nuclear retention of 40S markers (RpS2-GFP, RpS3-GFP). This places Ltv1 as required for cytoplasmic maturation of 40S subunits, with nuclear retention of pre-40S being a downstream consequence of failure to recycle factors.","method":"Dominant-negative mutagenesis, FISH, fluorescence microscopy (GFP-tagged ribosomal proteins), sucrose gradient sedimentation","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (FISH, live fluorescence imaging, sedimentation), single lab","pmids":["20215468"],"is_preprint":false},{"year":2014,"finding":"Ltv1 has a canonical leucine-rich NES at its extreme C-terminus that is both necessary for Crm1 interaction and for Ltv1 nuclear export. The C-terminus can functionally substitute for the NES of the 60S-export adapter Nmd3. However, deletion of the NES at endogenous levels complements slow growth and 40S biogenesis defects, suggesting Ltv1's export adapter function is fully redundant with other factors. Dominant-negative phenotype of NES-deleted Ltv1 overexpression is suppressed by co-overexpression of RpS3 and its chaperone Yar1, or by deleting the RpS3-binding site in Ltv1ΔNES, indicating that titration of RpS3 by excess nuclear Ltv1 is the deleterious mechanism.","method":"NES mutagenesis, Crm1 interaction assay, functional NES substitution, genetic suppression, overexpression complementation","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal genetic and biochemical methods, single lab","pmids":["25213169"],"is_preprint":false},{"year":2015,"finding":"Hrr25 (yeast CK1δ/ε homolog) phosphorylates Ltv1, causing its release from nascent pre-40S subunits and allowing subunit maturation. Hrr25 inactivation or expression of a non-phosphorylatable Ltv1 variant blocked Ltv1 release in vitro and in vivo and prevented entry into the translation-like quality control cycle. Phosphomimetic Ltv1 variants rescued viability after Hrr25 depletion. Ltv1 knockdown in human breast cancer cells impaired apoptosis induced by CK1δ/ε inhibitors, establishing that the antiproliferative activity of these inhibitors is due at least in part to disruption of ribosome assembly.","method":"In vitro phosphorylation assay, non-phosphorylatable and phosphomimetic mutants, genetic rescue, siRNA knockdown in human cancer cells, cell viability assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay, phosphomimetic/non-phosphorylatable mutagenesis, in vivo rescue, and human cell validation across multiple orthogonal methods","pmids":["25778921"],"is_preprint":false},{"year":2015,"finding":"Drosophila LTV1 interacts with ribosomal protein S3 and co-purifies with free 40S ribosome subunits. LTV1 is required for 40S ribosome subunit synthesis and pre-rRNA processing. dMyc directly regulates LTV1 transcription and requires LTV1 to stimulate ribosome biogenesis; loss of LTV1 blocks dMyc-induced cell growth and endoreplication.","method":"Co-immunoprecipitation, sucrose gradient fractionation, pre-rRNA processing assay, dMyc ChIP/transcriptional reporter, genetic epistasis (loss-of-function)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical interaction and functional epistasis demonstrated with multiple methods, single lab, Drosophila ortholog","pmids":["25858587"],"is_preprint":false},{"year":2018,"finding":"Ltv1 facilitates the incorporation of Rps3, Rps10, and Asc1/RACK1 into the small ribosomal subunit head, as shown by structure probing and biochemistry. Ribosomes from Ltv1-deficient yeast have substoichiometric amounts of Rps10 and Asc1 and show defects in translational fidelity and ribosome-mediated RNA quality control. Breast cancer cells have reduced LTV1 levels and produce ribosomes lacking RPS3, RPS10, and RACK1, connecting the chaperone mechanism to cancer cell ribosome diversity.","method":"Yeast genetics (deletion), mass spectrometry (quantitative ribosome composition), rRNA structure probing, translational fidelity assay, comparative analysis of human cancer cell lines","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (genetics, MS, structure probing, functional assays) in single rigorous study, with human cell validation","pmids":["30348748"],"is_preprint":false},{"year":2022,"finding":"A homozygous missense variant (c.503A>G, p.Asn168Ser) in LTV1 creates a new donor splice site, causing aberrant splicing and a premature termination codon in exon 6, as confirmed by minigene splicing assay in HEK293T cells and patient skin sample. This loss-of-function variant is linked to the LIPHAK ribosomopathy syndrome, establishing LTV1 as a disease gene in humans.","method":"Whole-genome sequencing, homozygosity mapping, minigene splicing assay (HEK293T and patient tissue)","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional splicing assay validated in two tissue contexts, single lab, disease mutation characterization","pmids":["34999892"],"is_preprint":false},{"year":2023,"finding":"Ltv1 directly binds 5 out of 15 ribosomal proteins in the small subunit head and indirectly affects 4 additional RPs via conformational transitions it regulates in the nascent subunit. Ltv1 aids recruitment of some RPs via direct protein-protein interactions while simultaneously delaying the recruitment of other RPs, thereby controlling hierarchical RP assembly. Delayed RP binding also delays acquisition of RNA structure stabilized by those RPs. Ltv1 directly chaperones folding of the three-helix junction j34-35-38 in rRNA. The LIPHAK disease-associated mutation causes global defects in head assembly consistent with these roles.","method":"Yeast genetics, mass spectrometry, DMS chemical probing (rRNA structure), biochemical interaction assays, disease-mutant analysis","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (genetics, MS, DMS probing, biochemistry) in single rigorous study with disease-mutant validation","pmids":["37910572"],"is_preprint":false}],"current_model":"LTV1 is a conserved 40S ribosome biogenesis assembly factor that binds pre-40S particles and chaperones hierarchical ribosomal protein (Rps3, Rps10, Asc1/RACK1, and others) incorporation and rRNA folding in the small subunit head; its release from nascent 40S subunits is triggered by phosphorylation by the CK1δ homolog Hrr25, which is required for subunit maturation and entry into the translation-like quality control cycle, and it also functions as a Crm1-dependent nuclear export adapter (though this function is redundant) for pre-40S particles."},"narrative":{"mechanistic_narrative":"LTV1 is a conserved 40S ribosome biogenesis assembly factor that binds nascent pre-40S particles and chaperones the hierarchical maturation of the small subunit head [PMID:16888326, PMID:30348748, PMID:37910572]. It directly binds several head ribosomal proteins and facilitates the ordered incorporation of Rps3, Rps10, and Asc1/RACK1, while simultaneously delaying the recruitment of other proteins, thereby controlling the timing of both RP assembly and the acquisition of the rRNA structures those proteins stabilize; it also directly chaperones folding of the j34-35-38 three-helix junction in rRNA [PMID:30348748, PMID:37910572]. Ribosomes formed in the absence of LTV1 are substoichiometric for Rps10 and Asc1 and show defects in translational fidelity and ribosome-mediated RNA quality control [PMID:30348748]. Release of Ltv1 from nascent pre-40S subunits is triggered by phosphorylation by Hrr25 (the yeast CK1δ/ε homolog), a step required for subunit maturation and entry into the translation-like quality control cycle [PMID:25778921]. Ltv1 additionally serves as a Crm1-dependent nuclear export adapter for the small subunit through a C-terminal leucine-rich NES, but this export function is redundant with other adapters at endogenous expression levels [PMID:16888326, PMID:25213169]. Across species the protein supports growth-coupled ribosome production — in Drosophila it is a direct dMyc transcriptional target required for Myc-driven ribosome biogenesis and cell growth [PMID:25858587] — and a loss-of-function splicing variant in human LTV1 causes the LIPHAK ribosomopathy syndrome [PMID:34999892, PMID:37910572].","teleology":[{"year":2004,"claim":"Established that Ltv1 is a bona fide 40S production factor rather than a generic ribosome-associated protein, by showing it physically partners with RpS3/Yar1 in a pre-40S complex and its loss selectively reduces 40S subunits.","evidence":"Co-immunoprecipitation, polysome profiling, and genetic suppression in yeast","pmids":["15611164"],"confidence":"Medium","gaps":["Did not define the molecular step Ltv1 performs in assembly","RpS3 overexpression failed to suppress, leaving Ltv1's distinct function unexplained"]},{"year":2006,"claim":"Identified a nuclear export role by showing Ltv1 shuttles in a Crm1-dependent manner via a functional NES and links the export machinery to the small subunit, addressing how pre-40S particles reach the cytoplasm.","evidence":"Sucrose gradient co-sedimentation, shuttling/export reporter assay, FISH localization, and YRB2 genetic interaction in yeast","pmids":["16888326"],"confidence":"High","gaps":["Did not establish whether the export adapter role is the essential function of Ltv1","Cytoplasmic maturation steps not resolved"]},{"year":2010,"claim":"Showed that Ltv1 is required for cytoplasmic maturation of 40S subunits and that nuclear retention of pre-40S in NES-defective mutants is a downstream consequence of failed factor recycling, refining the order of events.","evidence":"Dominant-negative NES mutagenesis, FISH, GFP-tagged RP imaging, and sedimentation in yeast","pmids":["20215468"],"confidence":"Medium","gaps":["Mechanism triggering Ltv1 release from the subunit unknown","Did not separate export from cytoplasmic maturation contributions"]},{"year":2014,"claim":"Resolved the significance of the export function by mapping a canonical C-terminal NES and showing that at endogenous levels its export adapter role is fully redundant, with RpS3 titration explaining the dominant-negative phenotype.","evidence":"NES mutagenesis, Crm1 interaction assay, functional NES substitution for Nmd3, and genetic suppression in yeast","pmids":["25213169"],"confidence":"Medium","gaps":["Did not identify the redundant export adapters","Essential, non-redundant function of Ltv1 remained undefined"]},{"year":2015,"claim":"Defined the regulatory trigger for Ltv1 release by showing Hrr25/CK1δ phosphorylation drives its dissociation and licenses maturation, and connected this to the antiproliferative action of CK1 inhibitors in human cancer cells.","evidence":"In vitro kinase assay, non-phosphorylatable and phosphomimetic mutants, genetic rescue in yeast, and siRNA knockdown/viability in human breast cancer cells","pmids":["25778921"],"confidence":"High","gaps":["Did not map which Ltv1 residues are phosphorylated structurally","How phosphorylation alters Ltv1-subunit contacts not resolved"]},{"year":2015,"claim":"Placed LTV1 in a growth-control circuit by showing the Drosophila ortholog is a direct dMyc transcriptional target required for Myc-driven ribosome biogenesis and cell growth.","evidence":"Co-IP, sucrose gradient fractionation, pre-rRNA processing, dMyc ChIP/reporter, and loss-of-function epistasis in Drosophila","pmids":["25858587"],"confidence":"Medium","gaps":["Whether Myc regulates LTV1 in mammals not tested","Conservation of the growth-coupling circuit to humans unaddressed"]},{"year":2018,"claim":"Defined the chaperone mechanism by demonstrating Ltv1 facilitates incorporation of Rps3, Rps10, and Asc1/RACK1 into the head, with functional consequences for translational fidelity and a link to altered ribosome composition in cancer cells.","evidence":"Yeast deletion genetics, quantitative MS of ribosome composition, rRNA structure probing, translational fidelity assays, and human cancer cell line analysis","pmids":["30348748"],"confidence":"High","gaps":["Direct vs indirect contributions to each RP not separated","Structural basis of head chaperoning not yet mapped"]},{"year":2022,"claim":"Established LTV1 as a human disease gene by showing a homozygous splice-altering variant produces a loss-of-function allele underlying the LIPHAK ribosomopathy syndrome.","evidence":"Whole-genome sequencing, homozygosity mapping, and minigene splicing assay in HEK293T and patient tissue","pmids":["34999892"],"confidence":"Medium","gaps":["Did not connect the variant to a specific molecular ribosome assembly defect","Genotype-phenotype basis of LIPHAK features not mechanistically explained"]},{"year":2023,"claim":"Provided a mechanistic model of hierarchical assembly control by showing Ltv1 directly binds 5 head RPs, delays recruitment of others, and chaperones a specific rRNA three-helix junction, and connected the disease mutation to global head assembly defects.","evidence":"Yeast genetics, MS, DMS chemical rRNA probing, biochemical interaction assays, and disease-mutant analysis","pmids":["37910572"],"confidence":"High","gaps":["High-resolution structure of the Ltv1-pre-40S complex not reported","How delayed RP recruitment is mechanistically enforced not fully resolved"]},{"year":null,"claim":"How LTV1 loss-of-function gives rise to the specific tissue phenotypes of LIPHAK, and whether its head-assembly chaperone role couples to oncogenic ribosome heterogeneity in human tissues, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the human LTV1-pre-40S complex","Tissue-specific consequences of altered ribosome composition unresolved","Direct link between LIPHAK variant and translational defects in patients not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[6,8]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[8]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,6,8]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,6]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,3]}],"complexes":["pre-40S ribosomal particle"],"partners":["RPS3","RPS10","RACK1","YAR1","HRR25","CRM1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96GA3","full_name":"Protein LTV1 homolog","aliases":[],"length_aa":475,"mass_kda":54.9,"function":"Essential for ribosome biogenesis","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q96GA3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/LTV1","classification":"Common Essential","n_dependent_lines":1088,"n_total_lines":1208,"dependency_fraction":0.9006622516556292},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000135521","cell_line_id":"CID001068","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleolus_gc","grade":1},{"compartment":"nucleoplasm","grade":1}],"interactors":[{"gene":"BYSL","stoichiometry":10.0},{"gene":"TSR1","stoichiometry":10.0},{"gene":"NOB1","stoichiometry":10.0},{"gene":"PNO1","stoichiometry":10.0},{"gene":"RIOK3","stoichiometry":10.0},{"gene":"RIOK2","stoichiometry":4.0},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CSNK2A1","stoichiometry":0.2},{"gene":"CSNK2A2","stoichiometry":0.2},{"gene":"DNAJC2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001068","total_profiled":1310},"omim":[{"mim_id":"620199","title":"INFLAMMATORY POIKILODERMA WITH HAIR ABNORMALITIES AND ACRAL KERATOSES; IPHAK","url":"https://www.omim.org/entry/620199"},{"mim_id":"620074","title":"LTV1 RIBOSOME BIOGENESIS FACTOR; LTV1","url":"https://www.omim.org/entry/620074"},{"mim_id":"618710","title":"PARTNER OF NOB1; PNO1","url":"https://www.omim.org/entry/618710"},{"mim_id":"617754","title":"RIO KINASE 2; RIOK2","url":"https://www.omim.org/entry/617754"},{"mim_id":"617753","title":"RIO KINASE 1; RIOK1","url":"https://www.omim.org/entry/617753"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Cytosol","reliability":"Enhanced"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/LTV1"},"hgnc":{"alias_symbol":["FLJ14909","dJ468K18.4"],"prev_symbol":["C6orf93"]},"alphafold":{"accession":"Q96GA3","domains":[{"cath_id":"-","chopping":"8-69_102-127","consensus_level":"medium","plddt":84.1651,"start":8,"end":127}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96GA3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96GA3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96GA3-F1-predicted_aligned_error_v6.png","plddt_mean":68.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LTV1","jax_strain_url":"https://www.jax.org/strain/search?query=LTV1"},"sequence":{"accession":"Q96GA3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96GA3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96GA3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96GA3"}},"corpus_meta":[{"pmid":"16888326","id":"PMC_16888326","title":"Ltv1 is required for efficient nuclear export of the ribosomal small subunit in Saccharomyces cerevisiae.","date":"2006","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16888326","citation_count":73,"is_preprint":false},{"pmid":"25778921","id":"PMC_25778921","title":"Hrr25/CK1δ-directed release of Ltv1 from pre-40S ribosomes is necessary for ribosome assembly and cell growth.","date":"2015","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/25778921","citation_count":68,"is_preprint":false},{"pmid":"15611164","id":"PMC_15611164","title":"Genetic and biochemical interactions among Yar1, Ltv1 and Rps3 define novel links between environmental stress and ribosome biogenesis in Saccharomyces cerevisiae.","date":"2004","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/15611164","citation_count":50,"is_preprint":false},{"pmid":"30348748","id":"PMC_30348748","title":"Ribosome biogenesis factor Ltv1 chaperones the assembly of the small subunit head.","date":"2018","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/30348748","citation_count":34,"is_preprint":false},{"pmid":"20215468","id":"PMC_20215468","title":"Dominant mutations in the late 40S biogenesis factor Ltv1 affect cytoplasmic maturation of the small ribosomal subunit in Saccharomyces cerevisiae.","date":"2010","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20215468","citation_count":26,"is_preprint":false},{"pmid":"25213169","id":"PMC_25213169","title":"Genetic analysis of the ribosome biogenesis factor Ltv1 of Saccharomyces cerevisiae.","date":"2014","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25213169","citation_count":19,"is_preprint":false},{"pmid":"25858587","id":"PMC_25858587","title":"Drosophila Low Temperature Viability Protein 1 (LTV1) Is Required for Ribosome Biogenesis and Cell Growth Downstream of Drosophila Myc (dMyc).","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25858587","citation_count":8,"is_preprint":false},{"pmid":"34692673","id":"PMC_34692673","title":"The Ribosome Biogenesis Factor Ltv1 Is Essential for Digestive Organ Development and Definitive Hematopoiesis in Zebrafish.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34692673","citation_count":6,"is_preprint":false},{"pmid":"34999892","id":"PMC_34999892","title":"Mutations in the ribosome biogenesis factor gene LTV1 are linked to LIPHAK syndrome, a novel poikiloderma-like disorder.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34999892","citation_count":5,"is_preprint":false},{"pmid":"37910572","id":"PMC_37910572","title":"A disease associated mutant reveals how Ltv1 orchestrates RP assembly and rRNA folding of the small ribosomal subunit head.","date":"2023","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37910572","citation_count":5,"is_preprint":false},{"pmid":"37503067","id":"PMC_37503067","title":"A disease associated mutant reveals how Ltv1 orchestrates RP assembly and rRNA folding of the small ribosomal subunit head.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37503067","citation_count":0,"is_preprint":false},{"pmid":"25657348","id":"PMC_25657348","title":"Location is everything: an educational primer for use with \"genetic analysis of the ribosome biogenesis factor Ltv1 of Saccharomyces cerevisiae\".","date":"2015","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25657348","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7731,"output_tokens":2822,"usd":0.032761,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10141,"output_tokens":3440,"usd":0.068352,"stage2_stop_reason":"end_turn"},"total_usd":0.101113,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"Ltv1 shuttles between nucleus and cytoplasm in a Crm1-dependent manner and contains a functional nuclear export sequence (NES) sufficient to direct export of an NLS-containing reporter. Ltv1 co-sediments with 43S/40S subunits and copurifies with late 43S particles. Loss of LTV1 reduces small subunit export as judged by altered distribution of 5'-ITS1 rRNA and RpS3. Genetic interaction was identified between LTV1 and YRB2 (a Ran-GTP/Crm1-binding protein), placing Ltv1 as an adapter linking nuclear export machinery to the small subunit.\",\n      \"method\": \"Sucrose gradient co-sedimentation, copurification, shuttling assay (heterokaryon/reporter), FISH/fluorescence localization, genetic interaction analysis\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biochemical co-sedimentation, export reporter assay, localization, genetic epistasis) replicated across multiple experiments in one study, with additional genetic corroboration\",\n      \"pmids\": [\"16888326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Ltv1 physically interacts with Yar1 (an ankyrin-repeat protein) and RpS3 as part of a pre-40S complex. Loss of LTV1 results in reduced absolute numbers of 40S subunits and excess free 60S subunits, indicating a role in 40S subunit production. Overexpression of RPS3 does not suppress the ribosome biogenesis defect of Δltv1, distinguishing Ltv1's role from that of Yar1.\",\n      \"method\": \"Co-immunoprecipitation, polysome profiling, genetic suppression analysis\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal genetic and biochemical interactions shown, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"15611164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mutation or deletion of the putative NES in Ltv1 is strongly dominant negative; the dominant-negative mutant protein accumulates in the cytoplasm associated with pre-40S subunits, causes accumulation of 20S rRNA in the cytoplasm (detected by FISH), retains late biogenesis factor Tsr1 in the cytoplasm, and leads to nuclear retention of 40S markers (RpS2-GFP, RpS3-GFP). This places Ltv1 as required for cytoplasmic maturation of 40S subunits, with nuclear retention of pre-40S being a downstream consequence of failure to recycle factors.\",\n      \"method\": \"Dominant-negative mutagenesis, FISH, fluorescence microscopy (GFP-tagged ribosomal proteins), sucrose gradient sedimentation\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (FISH, live fluorescence imaging, sedimentation), single lab\",\n      \"pmids\": [\"20215468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ltv1 has a canonical leucine-rich NES at its extreme C-terminus that is both necessary for Crm1 interaction and for Ltv1 nuclear export. The C-terminus can functionally substitute for the NES of the 60S-export adapter Nmd3. However, deletion of the NES at endogenous levels complements slow growth and 40S biogenesis defects, suggesting Ltv1's export adapter function is fully redundant with other factors. Dominant-negative phenotype of NES-deleted Ltv1 overexpression is suppressed by co-overexpression of RpS3 and its chaperone Yar1, or by deleting the RpS3-binding site in Ltv1ΔNES, indicating that titration of RpS3 by excess nuclear Ltv1 is the deleterious mechanism.\",\n      \"method\": \"NES mutagenesis, Crm1 interaction assay, functional NES substitution, genetic suppression, overexpression complementation\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal genetic and biochemical methods, single lab\",\n      \"pmids\": [\"25213169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hrr25 (yeast CK1δ/ε homolog) phosphorylates Ltv1, causing its release from nascent pre-40S subunits and allowing subunit maturation. Hrr25 inactivation or expression of a non-phosphorylatable Ltv1 variant blocked Ltv1 release in vitro and in vivo and prevented entry into the translation-like quality control cycle. Phosphomimetic Ltv1 variants rescued viability after Hrr25 depletion. Ltv1 knockdown in human breast cancer cells impaired apoptosis induced by CK1δ/ε inhibitors, establishing that the antiproliferative activity of these inhibitors is due at least in part to disruption of ribosome assembly.\",\n      \"method\": \"In vitro phosphorylation assay, non-phosphorylatable and phosphomimetic mutants, genetic rescue, siRNA knockdown in human cancer cells, cell viability assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay, phosphomimetic/non-phosphorylatable mutagenesis, in vivo rescue, and human cell validation across multiple orthogonal methods\",\n      \"pmids\": [\"25778921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Drosophila LTV1 interacts with ribosomal protein S3 and co-purifies with free 40S ribosome subunits. LTV1 is required for 40S ribosome subunit synthesis and pre-rRNA processing. dMyc directly regulates LTV1 transcription and requires LTV1 to stimulate ribosome biogenesis; loss of LTV1 blocks dMyc-induced cell growth and endoreplication.\",\n      \"method\": \"Co-immunoprecipitation, sucrose gradient fractionation, pre-rRNA processing assay, dMyc ChIP/transcriptional reporter, genetic epistasis (loss-of-function)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical interaction and functional epistasis demonstrated with multiple methods, single lab, Drosophila ortholog\",\n      \"pmids\": [\"25858587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ltv1 facilitates the incorporation of Rps3, Rps10, and Asc1/RACK1 into the small ribosomal subunit head, as shown by structure probing and biochemistry. Ribosomes from Ltv1-deficient yeast have substoichiometric amounts of Rps10 and Asc1 and show defects in translational fidelity and ribosome-mediated RNA quality control. Breast cancer cells have reduced LTV1 levels and produce ribosomes lacking RPS3, RPS10, and RACK1, connecting the chaperone mechanism to cancer cell ribosome diversity.\",\n      \"method\": \"Yeast genetics (deletion), mass spectrometry (quantitative ribosome composition), rRNA structure probing, translational fidelity assay, comparative analysis of human cancer cell lines\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (genetics, MS, structure probing, functional assays) in single rigorous study, with human cell validation\",\n      \"pmids\": [\"30348748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A homozygous missense variant (c.503A>G, p.Asn168Ser) in LTV1 creates a new donor splice site, causing aberrant splicing and a premature termination codon in exon 6, as confirmed by minigene splicing assay in HEK293T cells and patient skin sample. This loss-of-function variant is linked to the LIPHAK ribosomopathy syndrome, establishing LTV1 as a disease gene in humans.\",\n      \"method\": \"Whole-genome sequencing, homozygosity mapping, minigene splicing assay (HEK293T and patient tissue)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional splicing assay validated in two tissue contexts, single lab, disease mutation characterization\",\n      \"pmids\": [\"34999892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Ltv1 directly binds 5 out of 15 ribosomal proteins in the small subunit head and indirectly affects 4 additional RPs via conformational transitions it regulates in the nascent subunit. Ltv1 aids recruitment of some RPs via direct protein-protein interactions while simultaneously delaying the recruitment of other RPs, thereby controlling hierarchical RP assembly. Delayed RP binding also delays acquisition of RNA structure stabilized by those RPs. Ltv1 directly chaperones folding of the three-helix junction j34-35-38 in rRNA. The LIPHAK disease-associated mutation causes global defects in head assembly consistent with these roles.\",\n      \"method\": \"Yeast genetics, mass spectrometry, DMS chemical probing (rRNA structure), biochemical interaction assays, disease-mutant analysis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (genetics, MS, DMS probing, biochemistry) in single rigorous study with disease-mutant validation\",\n      \"pmids\": [\"37910572\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LTV1 is a conserved 40S ribosome biogenesis assembly factor that binds pre-40S particles and chaperones hierarchical ribosomal protein (Rps3, Rps10, Asc1/RACK1, and others) incorporation and rRNA folding in the small subunit head; its release from nascent 40S subunits is triggered by phosphorylation by the CK1δ homolog Hrr25, which is required for subunit maturation and entry into the translation-like quality control cycle, and it also functions as a Crm1-dependent nuclear export adapter (though this function is redundant) for pre-40S particles.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LTV1 is a conserved 40S ribosome biogenesis assembly factor that binds nascent pre-40S particles and chaperones the hierarchical maturation of the small subunit head [#0, #6, #8]. It directly binds several head ribosomal proteins and facilitates the ordered incorporation of Rps3, Rps10, and Asc1/RACK1, while simultaneously delaying the recruitment of other proteins, thereby controlling the timing of both RP assembly and the acquisition of the rRNA structures those proteins stabilize; it also directly chaperones folding of the j34-35-38 three-helix junction in rRNA [#6, #8]. Ribosomes formed in the absence of LTV1 are substoichiometric for Rps10 and Asc1 and show defects in translational fidelity and ribosome-mediated RNA quality control [#6]. Release of Ltv1 from nascent pre-40S subunits is triggered by phosphorylation by Hrr25 (the yeast CK1\\u03b4/\\u03b5 homolog), a step required for subunit maturation and entry into the translation-like quality control cycle [#4]. Ltv1 additionally serves as a Crm1-dependent nuclear export adapter for the small subunit through a C-terminal leucine-rich NES, but this export function is redundant with other adapters at endogenous expression levels [#0, #3]. Across species the protein supports growth-coupled ribosome production \\u2014 in Drosophila it is a direct dMyc transcriptional target required for Myc-driven ribosome biogenesis and cell growth [#5] \\u2014 and a loss-of-function splicing variant in human LTV1 causes the LIPHAK ribosomopathy syndrome [#7, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that Ltv1 is a bona fide 40S production factor rather than a generic ribosome-associated protein, by showing it physically partners with RpS3/Yar1 in a pre-40S complex and its loss selectively reduces 40S subunits.\",\n      \"evidence\": \"Co-immunoprecipitation, polysome profiling, and genetic suppression in yeast\",\n      \"pmids\": [\"15611164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not define the molecular step Ltv1 performs in assembly\", \"RpS3 overexpression failed to suppress, leaving Ltv1's distinct function unexplained\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified a nuclear export role by showing Ltv1 shuttles in a Crm1-dependent manner via a functional NES and links the export machinery to the small subunit, addressing how pre-40S particles reach the cytoplasm.\",\n      \"evidence\": \"Sucrose gradient co-sedimentation, shuttling/export reporter assay, FISH localization, and YRB2 genetic interaction in yeast\",\n      \"pmids\": [\"16888326\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether the export adapter role is the essential function of Ltv1\", \"Cytoplasmic maturation steps not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed that Ltv1 is required for cytoplasmic maturation of 40S subunits and that nuclear retention of pre-40S in NES-defective mutants is a downstream consequence of failed factor recycling, refining the order of events.\",\n      \"evidence\": \"Dominant-negative NES mutagenesis, FISH, GFP-tagged RP imaging, and sedimentation in yeast\",\n      \"pmids\": [\"20215468\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism triggering Ltv1 release from the subunit unknown\", \"Did not separate export from cytoplasmic maturation contributions\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Resolved the significance of the export function by mapping a canonical C-terminal NES and showing that at endogenous levels its export adapter role is fully redundant, with RpS3 titration explaining the dominant-negative phenotype.\",\n      \"evidence\": \"NES mutagenesis, Crm1 interaction assay, functional NES substitution for Nmd3, and genetic suppression in yeast\",\n      \"pmids\": [\"25213169\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the redundant export adapters\", \"Essential, non-redundant function of Ltv1 remained undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the regulatory trigger for Ltv1 release by showing Hrr25/CK1\\u03b4 phosphorylation drives its dissociation and licenses maturation, and connected this to the antiproliferative action of CK1 inhibitors in human cancer cells.\",\n      \"evidence\": \"In vitro kinase assay, non-phosphorylatable and phosphomimetic mutants, genetic rescue in yeast, and siRNA knockdown/viability in human breast cancer cells\",\n      \"pmids\": [\"25778921\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map which Ltv1 residues are phosphorylated structurally\", \"How phosphorylation alters Ltv1-subunit contacts not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Placed LTV1 in a growth-control circuit by showing the Drosophila ortholog is a direct dMyc transcriptional target required for Myc-driven ribosome biogenesis and cell growth.\",\n      \"evidence\": \"Co-IP, sucrose gradient fractionation, pre-rRNA processing, dMyc ChIP/reporter, and loss-of-function epistasis in Drosophila\",\n      \"pmids\": [\"25858587\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Myc regulates LTV1 in mammals not tested\", \"Conservation of the growth-coupling circuit to humans unaddressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the chaperone mechanism by demonstrating Ltv1 facilitates incorporation of Rps3, Rps10, and Asc1/RACK1 into the head, with functional consequences for translational fidelity and a link to altered ribosome composition in cancer cells.\",\n      \"evidence\": \"Yeast deletion genetics, quantitative MS of ribosome composition, rRNA structure probing, translational fidelity assays, and human cancer cell line analysis\",\n      \"pmids\": [\"30348748\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect contributions to each RP not separated\", \"Structural basis of head chaperoning not yet mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established LTV1 as a human disease gene by showing a homozygous splice-altering variant produces a loss-of-function allele underlying the LIPHAK ribosomopathy syndrome.\",\n      \"evidence\": \"Whole-genome sequencing, homozygosity mapping, and minigene splicing assay in HEK293T and patient tissue\",\n      \"pmids\": [\"34999892\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not connect the variant to a specific molecular ribosome assembly defect\", \"Genotype-phenotype basis of LIPHAK features not mechanistically explained\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a mechanistic model of hierarchical assembly control by showing Ltv1 directly binds 5 head RPs, delays recruitment of others, and chaperones a specific rRNA three-helix junction, and connected the disease mutation to global head assembly defects.\",\n      \"evidence\": \"Yeast genetics, MS, DMS chemical rRNA probing, biochemical interaction assays, and disease-mutant analysis\",\n      \"pmids\": [\"37910572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the Ltv1-pre-40S complex not reported\", \"How delayed RP recruitment is mechanistically enforced not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How LTV1 loss-of-function gives rise to the specific tissue phenotypes of LIPHAK, and whether its head-assembly chaperone role couples to oncogenic ribosome heterogeneity in human tissues, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the human LTV1-pre-40S complex\", \"Tissue-specific consequences of altered ribosome composition unresolved\", \"Direct link between LIPHAK variant and translational defects in patients not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [6, 8]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 6, 8]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"complexes\": [\"pre-40S ribosomal particle\"],\n    \"partners\": [\"RPS3\", \"RPS10\", \"RACK1\", \"YAR1\", \"HRR25\", \"CRM1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}