{"gene":"EXOC1","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1998,"finding":"Yeast Sec3p (ortholog of EXOC1) localizes to the site of polarized exocytosis independently of secretory pathway function, the actin and septin cytoskeletons, and polarity establishment proteins, establishing it as a spatial landmark defining sites of exocytosis.","method":"GFP fusion live imaging, genetic epistasis with secretory and cytoskeletal mutants","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiment with functional consequence, replicated across multiple genetic backgrounds, foundational paper with 306 citations","pmids":["9491896"],"is_preprint":false},{"year":1997,"finding":"Yeast SEC3 (ortholog of EXOC1) is required for targeting or fusion of post-Golgi secretory vesicles to the plasma membrane, genetically interacts with profilin (PFY1), and is required for correct bud site selection in diploids; high-copy SEC3 suppresses sec5-24.","method":"Genetic screen, synthetic lethality, gene dosage suppression, temperature-sensitive allele analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal genetic methods, replicated in subsequent studies, 92 citations","pmids":["9247645"],"is_preprint":false},{"year":2004,"finding":"In budding yeast, Sec3p (EXOC1 ortholog) and Exo70p remain stably associated with the plasma membrane independently of actin, while other exocyst subunits (Sec5p, Sec6p, Sec8p, Sec10p, Sec15p, Exo84p) are delivered on secretory vesicles; exocyst assembly occurs when vesicle-borne subunits join Sec3p/Exo70p at the plasma membrane.","method":"FRAP, immunogold electron microscopy, epifluorescence video microscopy, actin disruption experiments","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal imaging and biochemical methods, replicated, 241 citations","pmids":["15583031"],"is_preprint":false},{"year":2008,"finding":"The N-terminus of yeast Sec3 (EXOC1 ortholog) directly interacts with phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) and with GTP-bound Cdc42; both interactions are required for Sec3 plasma membrane targeting, exocytosis, exocyst polarization, and normal cell morphogenesis.","method":"In vitro binding assays, site-directed mutagenesis of key residues, genetic analysis in yeast","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro binding with mutagenesis plus genetic validation, 206 citations","pmids":["18195105"],"is_preprint":false},{"year":2010,"finding":"Crystal structure of the yeast Sec3 N-terminal domain (EXOC1 ortholog) in complex with Rho1 at 2.6 Å reveals a pleckstrin homology (PH) fold; conserved basic residues form a PtdIns(4,5)P2-binding cleft, and residues Phe77, Ile115, Leu131 mediate binding to the hydrophobic surface around switch regions I and II of Rho1.","method":"X-ray crystallography, mutagenesis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation of interaction residues","pmids":["20062059"],"is_preprint":false},{"year":2001,"finding":"The mammalian exocyst complex, including human Sec3 (EXOC1), interacts with RalA in a GTP-dependent manner in brain nerve terminals, identifying EXOC1 as a mammalian homologue of yeast Sec3p and placing the exocyst as an effector of RalA signaling in directing exocytosis sites.","method":"GTP-dependent affinity pulldown from brain lysates, MALDI-TOF MS identification, Western blot","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal pulldown with MS identification in native brain tissue, single lab","pmids":["11406615"],"is_preprint":false},{"year":2001,"finding":"Human Sec3 (EXOC1) interacts with other exocyst subunits Sec5 and Sec8 in a yeast two-hybrid system; GFP-fusions of hSec3 are cytosolic in MDCK cells, and hSec3 lacks the Rho1-binding site present in yeast Sec3p.","method":"Yeast two-hybrid, GFP fusion expression in MDCK cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid plus cell imaging, single lab, partial mechanistic characterization","pmids":["11493706"],"is_preprint":false},{"year":2014,"finding":"Yeast Sec3p (EXOC1 ortholog) is the only exocyst subunit capable of recruiting secretory vesicles when ectopically targeted to mitochondria, establishing Sec3p's unique role in vesicle tethering; Rab GTPase Sec4p and its GEF Sec2p regulate exocyst complex assembly.","method":"Ectopic mitochondrial targeting assay, epistasis analysis, fluorescence microscopy","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — novel reconstitution-like ectopic targeting assay with clear functional readout and multiple subunit comparisons","pmids":["25232005"],"is_preprint":false},{"year":2017,"finding":"Yeast Sec3 (EXOC1 ortholog) directly interacts with the t-SNARE protein Sso2, promoting formation of the Sso2-Sec9 binary t-SNARE complex; crystal structure of the Sec3-Sso2 complex shows Sec3 binding induces conformational changes in Sso2 relieving its autoinhibition, thereby stimulating membrane fusion independently of vesicle tethering.","method":"Crystal structure, in vitro membrane fusion assay, site-directed mutagenesis, Co-IP","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with in vitro reconstituted membrane fusion assay and mutagenesis confirming functional separation from tethering","pmids":["28112172"],"is_preprint":false},{"year":2009,"finding":"Mammalian Sec3 (EXOC1) associates with a subset of exocyst complexes enriched at desmosomes; RNAi-mediated Sec3 knockdown specifically impairs desmosome morphology and function without affecting adherens junctions; membrane recruitment of Sec3 depends on cadherin-mediated adhesion but occurs later than Sec6 and Sec8.","method":"RNAi knockdown, immunofluorescence, co-immunoprecipitation, functional junction assays in epithelial cells","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — clean RNAi KD with specific phenotypic readout and Co-IP, single lab","pmids":["19889837"],"is_preprint":false},{"year":2009,"finding":"Human Sec3 (EXOC1) binds to the SH2 domain-binding motif of elongation factor 1α (EF1α) and sequesters it; this interaction suppresses flavivirus RNA transcription and translation. Flavivirus capsid protein (WNV/DENV C protein) binds to the first 15 amino acids of hSec3p to disrupt the hSec3p-EF1α complex.","method":"Yeast two-hybrid screen, mutagenesis, siRNA knockdown, viral replication assays","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — yeast two-hybrid plus mutagenesis with functional viral replication readout, single lab","pmids":["19889084"],"is_preprint":false},{"year":2013,"finding":"WNV and DENV capsid proteins interact physically with human Sec3 (EXOC1) and activate 20S proteasome chymotrypsin-like activity to degrade hSec3p post-transcriptionally; specific amino acids (14 of WNV C, 13 of DENV C) mediate C protein-hSec3p binding, and residues 109-114 (WNV) or 102-107 (DENV) constitute the degradation motif.","method":"Mutagenesis, co-immunoprecipitation, proteasome activity assays, siRNA knockdown","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — mutagenesis plus binding and proteasome activity assays, single lab","pmids":["23522008"],"is_preprint":false},{"year":2005,"finding":"Human/mouse Sec3 (EXOC1) physically interacts with the C-terminal tail of glycine transporter GLYT1 via pulldown and co-immunoprecipitation; coexpression with GLYT1 partially recruits Sec3-GFP to the plasma membrane; Sec3 increases GLYT1 transporter capacity, suggesting the exocyst promotes GLYT1 insertion into the plasma membrane.","method":"Yeast two-hybrid, pulldown, co-immunoprecipitation from rat brain, immunofluorescence, functional transport assay","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple binding methods plus functional transport assay, single lab","pmids":["16181645"],"is_preprint":false},{"year":2015,"finding":"Homozygous knockout of mouse Exoc1 (EXOC1 ortholog) causes peri-implantation lethality, establishing an essential role for EXOC1 in early mouse development.","method":"Knockout mouse generation, genetic rescue analysis, expression analysis in blastocysts","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific lethal phenotype and genetic rescue experiment confirming Exoc1 as causative gene","pmids":["26346620"],"is_preprint":false},{"year":2021,"finding":"EXOC1 promotes pseudopod formation in mouse spermatogonia by inactivating the Rho family GTPase Rac1, and functions in spermatocyte syncytia formation together with SNARE proteins STX2 and SNAP23.","method":"Conditional knockout mice, immunofluorescence, co-immunoprecipitation, Rac1 activity assay","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — KO with specific cellular phenotype and co-IP identifying interacting partners, single lab","pmids":["33973520"],"is_preprint":false},{"year":2025,"finding":"EXOC1 depletion from mouse oocytes impairs intra-oocyte trafficking of c-KIT and GDF9, causing their abnormal cytoplasmic retention, leading to defective oocyte re-awakening, impaired cyst breakdown, and complete female infertility; phenotype is shared with depletion of exocyst members EXOC3 and EXOC7.","method":"Oocyte-specific conditional knockout, immunofluorescence localization of c-KIT and GDF9, fertility assays, comparison with EXOC3/EXOC7 KO","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with specific trafficking phenotype validated with multiple exocyst subunits, single lab","pmids":["39833146"],"is_preprint":false},{"year":2021,"finding":"Sec3 (EXOC1) knockdown in mouse hippocampal neurons prevents neuronal polarization and axon formation; in utero electroporation knockdown disrupts cortical neuron migration and morphology during neocortex formation.","method":"siRNA knockdown in primary hippocampal cultures, in utero electroporation, immunofluorescence","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with specific polarization and migration phenotypes in two independent neuronal systems","pmids":["34862972"],"is_preprint":false},{"year":2019,"finding":"Sec3 (EXOC1) knockdown in A549 lung cancer cells abolishes TGF-β-stimulated cell migration and EMT, and specifically inhibits TGF-β-stimulated Akt phosphorylation without affecting Smad2 phosphorylation; these defects are rescued by RNAi-resistant Sec3.","method":"siRNA knockdown, rescue with RNAi-resistant construct, Western blot for pAkt/pSmad2, wound healing assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — KD with rescue experiment and pathway-specific phosphorylation readout, single lab","pmids":["31495494"],"is_preprint":false},{"year":2012,"finding":"Fission yeast Sec3 (EXOC1 ortholog) physically interacts with the formin For3; sec3 deletion causes loss of actin cables due to failure to polarize For3, and also disrupts actin patch polarity and actomyosin ring constriction/disassembly; human Sec3/EXOC1 rescues fission yeast sec3 mutants.","method":"Co-immunoprecipitation, FRAP, genetic deletion analysis, heterologous complementation with human EXOC1","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus genetic analysis plus human ortholog rescue confirming conservation, single lab","pmids":["22891673"],"is_preprint":false},{"year":2007,"finding":"In Candida albicans, Sec3p (EXOC1 ortholog) is required for maintenance of hyphal tip growth after septin ring formation; the septin Cdc3p co-immunoprecipitates with Sec3p and Sec5p; deletion of septins Cdc10 or Cdc11 mislocalizes Sec3p and restores hyphal development in sec3Δ mutants, establishing a functional link between septins and exocyst-mediated polarized exocytosis.","method":"Co-immunoprecipitation, genetic deletion epistasis, fluorescence microscopy","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus genetic epistasis with clear phenotypic readout, single lab","pmids":["17504812"],"is_preprint":false},{"year":2017,"finding":"In fission yeast, Sec3 (EXOC1 ortholog) degradation is regulated by the ubiquitin-proteasome system via the E3 ubiquitin ligase Pib1 and deubiquitylase Ubp3; blocking the proteasome or Hsp70-type chaperones suppresses sec3 mutant phenotypes including defects in exocytosis, endocytosis, and cell septation.","method":"Extragenic suppressor screen, proteasome inhibition, genetic analysis with E3 ligase and deubiquitylase mutants","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — suppressor screen with multiple pathway components validated, single lab","pmids":["28765280"],"is_preprint":false}],"current_model":"EXOC1 (Sec3) is a subunit of the octameric exocyst complex that functions as both a spatial landmark and active regulator of polarized exocytosis: its PH-like N-terminal domain anchors it stably at the plasma membrane via direct binding to PtdIns(4,5)P2 and Rho-family GTPases (Cdc42/Rho1), it uniquely recruits secretory vesicles to tethering sites while other exocyst subunits arrive on vesicles, and it directly promotes SNARE complex assembly by binding t-SNARE Sso2 and relieving its autoinhibition to stimulate membrane fusion; in mammals, EXOC1 is essential for peri-implantation development, spermatogenesis (via Rac1 inactivation and SNARE interactions), oocyte trafficking of c-KIT and GDF9, desmosome assembly, neuronal polarization, and TGF-β/Akt-dependent cell migration."},"narrative":{"teleology":[{"year":1997,"claim":"The initial question was whether Sec3 functions in exocytosis; genetic analysis established that SEC3 is required for post-Golgi vesicle targeting or fusion at the plasma membrane and genetically interacts with cytoskeletal regulators.","evidence":"Temperature-sensitive alleles, synthetic lethality with profilin, gene dosage suppression in budding yeast","pmids":["9247645"],"confidence":"High","gaps":["No biochemical mechanism identified","No distinction between tethering and fusion roles"]},{"year":1998,"claim":"A central question was how exocytic sites are spatially specified; live imaging revealed that Sec3p localizes to polarized growth sites independently of the secretory pathway, actin, and septins, establishing it as a unique spatial landmark among exocyst subunits.","evidence":"GFP-Sec3 imaging across multiple yeast secretory and cytoskeletal mutants","pmids":["9491896"],"confidence":"High","gaps":["Mechanism of membrane targeting unknown","Whether mammalian EXOC1 behaves identically unclear"]},{"year":2001,"claim":"The mammalian EXOC1 ortholog was identified as a component of the exocyst complex in brain, linking it to RalA GTPase signaling, and initial characterization showed human Sec3 differs from yeast Sec3 in lacking the Rho1-binding site and displaying cytosolic localization in epithelial cells.","evidence":"GTP-dependent pulldown with MALDI-TOF MS from rat brain; yeast two-hybrid with exocyst subunits; GFP imaging in MDCK cells","pmids":["11406615","11493706"],"confidence":"Medium","gaps":["Mammalian membrane targeting mechanism unresolved","Functional role of mammalian EXOC1 not yet tested by loss-of-function"]},{"year":2004,"claim":"The question of how the exocyst assembles was addressed by showing Sec3p and Exo70p remain stably at the plasma membrane while six other subunits arrive on secretory vesicles, defining a two-pool assembly model.","evidence":"FRAP, immunogold EM, and video microscopy with actin disruption in budding yeast","pmids":["15583031"],"confidence":"High","gaps":["Structural basis of subunit-subunit assembly not resolved","Whether this model applies in mammalian cells unclear"]},{"year":2008,"claim":"The molecular basis of Sec3 membrane anchoring was resolved: the N-terminus directly binds PtdIns(4,5)P2 and GTP-Cdc42, and both interactions are required for polarized localization and exocytosis.","evidence":"In vitro lipid/GTPase binding assays with point mutagenesis and genetic validation in yeast","pmids":["18195105"],"confidence":"High","gaps":["Atomic details of dual-lipid/GTPase recognition not yet available"]},{"year":2010,"claim":"Structural determination of the Sec3 N-terminal domain in complex with Rho1 revealed a PH fold with a PtdIns(4,5)P2-binding basic cleft and a hydrophobic interface for Rho GTPase recognition, providing the atomic framework for membrane targeting.","evidence":"2.6 Å crystal structure with mutagenesis validation","pmids":["20062059"],"confidence":"High","gaps":["Full-length Sec3 structure not determined","No structure of the mammalian EXOC1 domain"]},{"year":2007,"claim":"Sec3 was linked to septin-dependent polarity control: in C. albicans, Sec3p co-immunoprecipitates with septins and is required for hyphal tip growth after septin ring formation, with septin deletion epistatic to sec3Δ.","evidence":"Co-IP and genetic epistasis with fluorescence microscopy in C. albicans","pmids":["17504812"],"confidence":"Medium","gaps":["Direct versus indirect septin–Sec3 interaction not distinguished","Relevance to mammalian septins untested"]},{"year":2009,"claim":"Mammalian EXOC1 was found to have a specific role in desmosome assembly: Sec3 knockdown impairs desmosome but not adherens junction integrity, and Sec3 is recruited to cell–cell contacts in a cadherin-dependent manner.","evidence":"RNAi, co-IP, and functional junction assays in epithelial cells","pmids":["19889837"],"confidence":"Medium","gaps":["Cargo delivered by EXOC1-containing exocyst to desmosomes not identified","Whether EXOC1 acts as a full-complex subunit or sub-complex at desmosomes unclear"]},{"year":2012,"claim":"Sec3 was shown to physically interact with the formin For3 in fission yeast and is required for actin cable polarization; human EXOC1 rescues fission yeast sec3 mutants, demonstrating functional conservation.","evidence":"Co-IP, FRAP, genetic deletion, and heterologous complementation","pmids":["22891673"],"confidence":"Medium","gaps":["Binding interface between Sec3 and formin not mapped","Whether EXOC1 regulates mammalian formins untested"]},{"year":2014,"claim":"Among all eight exocyst subunits, only Sec3 can recruit secretory vesicles when ectopically targeted to mitochondria, resolving the question of which subunit initiates vesicle tethering.","evidence":"Ectopic mitochondrial targeting assay with fluorescence microscopy in yeast","pmids":["25232005"],"confidence":"High","gaps":["Molecular basis of Sec3's unique vesicle-recruiting capability not identified","Whether this applies in mammalian cells unknown"]},{"year":2015,"claim":"Homozygous Exoc1 knockout in mice causes peri-implantation lethality, establishing EXOC1 as essential for early mammalian development.","evidence":"Constitutive knockout mouse with genetic rescue","pmids":["26346620"],"confidence":"High","gaps":["Specific developmental process requiring EXOC1 at peri-implantation not identified","Cell-type-specific requirements not dissected"]},{"year":2017,"claim":"Sec3 was shown to directly promote SNARE-mediated membrane fusion by binding t-SNARE Sso2 and relieving its autoinhibition, establishing a fusion-promoting function mechanistically separable from vesicle tethering.","evidence":"Crystal structure of Sec3–Sso2 complex, in vitro reconstituted membrane fusion assay, mutagenesis","pmids":["28112172"],"confidence":"High","gaps":["Whether mammalian EXOC1 similarly activates cognate t-SNAREs not tested","Integration of tethering and fusion-promoting activities in vivo not resolved"]},{"year":2017,"claim":"Sec3 protein turnover was found to be regulated by the ubiquitin-proteasome system via E3 ligase Pib1 and deubiquitylase Ubp3, connecting protein quality control to exocyst function.","evidence":"Extragenic suppressor screen with proteasome inhibition and genetic analysis in fission yeast","pmids":["28765280"],"confidence":"Medium","gaps":["Ubiquitylation sites on Sec3 not mapped","Whether mammalian EXOC1 turnover is similarly regulated unknown"]},{"year":2019,"claim":"EXOC1 was placed in TGF-β signaling: Sec3 knockdown abolishes TGF-β-stimulated Akt phosphorylation and cell migration without affecting Smad2 signaling, identifying EXOC1 as a pathway-selective mediator of non-canonical TGF-β signaling.","evidence":"siRNA knockdown with RNAi-resistant rescue, Western blot, wound healing assay in A549 cells","pmids":["31495494"],"confidence":"Medium","gaps":["Mechanism by which EXOC1 selectively modulates Akt signaling unknown","Only tested in one cancer cell line"]},{"year":2021,"claim":"Conditional knockout studies established EXOC1 as essential for spermatogenesis, where it promotes pseudopod formation via Rac1 inactivation and spermatocyte syncytia formation through interaction with SNARE proteins STX2 and SNAP23, and for neuronal polarization and cortical migration.","evidence":"Conditional knockout mice with Rac1 activity assays and co-IP (spermatogenesis); siRNA and in utero electroporation (neurons)","pmids":["33973520","34862972"],"confidence":"Medium","gaps":["Whether EXOC1 directly inhibits Rac1 or acts through a GAP not determined","Cargo delivered during neuronal polarization not identified"]},{"year":2025,"claim":"EXOC1 depletion from oocytes impairs intra-oocyte trafficking of c-KIT and GDF9, causing their cytoplasmic retention and leading to defective cyst breakdown and female infertility, extending the mammalian EXOC1 requirement to oogenesis.","evidence":"Oocyte-specific conditional knockout with immunofluorescence and fertility assays in mice","pmids":["39833146"],"confidence":"Medium","gaps":["Whether EXOC1 directly traffics c-KIT/GDF9 or acts indirectly through general exocytic machinery unclear","Single lab finding"]},{"year":null,"claim":"Major open questions include the structure of full-length mammalian EXOC1, whether mammalian EXOC1 directly activates cognate t-SNAREs as yeast Sec3 does, the identity of specific cargo delivered by EXOC1-containing exocyst subcomplexes in different mammalian cell types, and the mechanism by which EXOC1 selectively modulates non-canonical TGF-β/Akt signaling.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length mammalian EXOC1 structure","No in vitro reconstitution of mammalian EXOC1-SNARE activation","Cargo specificity in distinct mammalian tissues unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,14]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,3,4]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,2,7,8]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[12,15]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,17]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[13,14,16]}],"complexes":["exocyst complex"],"partners":["EXOC2","EXOC3","STX2","SNAP23","RALA","CDC42","RAC1","EEF1A1"],"other_free_text":[]},"mechanistic_narrative":"EXOC1 (Sec3) is a subunit of the octameric exocyst complex that serves as a spatial landmark for polarized exocytosis and actively promotes membrane fusion. In yeast, Sec3 localizes to exocytic sites independently of the secretory pathway and actin cytoskeleton, where its PH-domain N-terminus binds PtdIns(4,5)P2 and Rho-family GTPases (Cdc42, Rho1) to anchor the complex at the plasma membrane, and it is the only exocyst subunit capable of recruiting secretory vesicles when ectopically targeted [PMID:9491896, PMID:18195105, PMID:20062059, PMID:25232005]. Sec3 also directly binds the t-SNARE Sso2, relieving its autoinhibition to stimulate SNARE complex assembly and membrane fusion independently of its tethering function [PMID:28112172]. In mammals, EXOC1 is essential for peri-implantation development, and conditional loss-of-function studies demonstrate requirements in spermatogenesis via Rac1 inactivation and SNARE interactions, oocyte trafficking of c-KIT and GDF9, desmosome assembly, neuronal polarization, and TGF-β/Akt-dependent cell migration [PMID:26346620, PMID:33973520, PMID:39833146, PMID:19889837, PMID:34862972, PMID:31495494]."},"prefetch_data":{"uniprot":{"accession":"Q9NV70","full_name":"Exocyst complex component 1","aliases":["Exocyst complex component Sec3"],"length_aa":894,"mass_kda":102.0,"function":"Component of the exocyst complex involved in the docking of exocytic vesicles with fusion sites on the plasma membrane (Microbial infection) Has an antiviral effect against flaviviruses by affecting viral RNA transcription and translation through the sequestration of elongation factor 1-alpha (EEF1A1). This results in decreased viral RNA synthesis and decreased viral protein translation","subcellular_location":"Midbody, Midbody ring; Cytoplasm; Cytoplasm, perinuclear region; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9NV70/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/EXOC1","classification":"Common Essential","n_dependent_lines":703,"n_total_lines":1208,"dependency_fraction":0.581953642384106},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/EXOC1","total_profiled":1310},"omim":[{"mim_id":"618934","title":"COILED-COIL SERINE-RICH PROTEIN 1; CCSER1","url":"https://www.omim.org/entry/618934"},{"mim_id":"607879","title":"EXOCYST COMPLEX COMPONENT 1; EXOC1","url":"https://www.omim.org/entry/607879"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Plasma membrane","reliability":"Uncertain"},{"location":"Microtubules","reliability":"Uncertain"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EXOC1"},"hgnc":{"alias_symbol":["SEC3","FLJ10893","BM-102","Sec3p"],"prev_symbol":["SEC3L1"]},"alphafold":{"accession":"Q9NV70","domains":[{"cath_id":"2.30.29.90","chopping":"1-137","consensus_level":"medium","plddt":87.06,"start":1,"end":137},{"cath_id":"-","chopping":"775-892","consensus_level":"high","plddt":85.106,"start":775,"end":892},{"cath_id":"1.20.5","chopping":"205-280","consensus_level":"medium","plddt":87.7482,"start":205,"end":280}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NV70","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NV70-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NV70-F1-predicted_aligned_error_v6.png","plddt_mean":79.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EXOC1","jax_strain_url":"https://www.jax.org/strain/search?query=EXOC1"},"sequence":{"accession":"Q9NV70","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NV70.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NV70/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NV70"}},"corpus_meta":[{"pmid":"9491896","id":"PMC_9491896","title":"Sec3p is a spatial landmark for polarized secretion in budding yeast.","date":"1998","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/9491896","citation_count":306,"is_preprint":false},{"pmid":"15583031","id":"PMC_15583031","title":"Vesicles carry most exocyst subunits to exocytic sites marked by the remaining two subunits, Sec3p and Exo70p.","date":"2004","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/15583031","citation_count":241,"is_preprint":false},{"pmid":"18195105","id":"PMC_18195105","title":"Membrane association and functional regulation of Sec3 by phospholipids and Cdc42.","date":"2008","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/18195105","citation_count":206,"is_preprint":false},{"pmid":"15980192","id":"PMC_15980192","title":"The roothairless1 gene of maize encodes a homolog of sec3, which is involved in polar exocytosis.","date":"2005","source":"Plant physiology","url":"https://pubmed.ncbi.nlm.nih.gov/15980192","citation_count":132,"is_preprint":false},{"pmid":"11406615","id":"PMC_11406615","title":"The brain exocyst complex interacts with RalA in a GTP-dependent manner: identification of a novel mammalian Sec3 gene and a second Sec15 gene.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11406615","citation_count":119,"is_preprint":false},{"pmid":"11493706","id":"PMC_11493706","title":"The Sec6/8 complex in mammalian cells: characterization of mammalian Sec3, subunit interactions, and expression of subunits in polarized cells.","date":"2001","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/11493706","citation_count":95,"is_preprint":false},{"pmid":"9247645","id":"PMC_9247645","title":"Sec3p is involved in secretion and morphogenesis in Saccharomyces cerevisiae.","date":"1997","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/9247645","citation_count":92,"is_preprint":false},{"pmid":"20062059","id":"PMC_20062059","title":"Structural basis for the Rho- and phosphoinositide-dependent localization of the exocyst subunit Sec3.","date":"2010","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/20062059","citation_count":85,"is_preprint":false},{"pmid":"27516531","id":"PMC_27516531","title":"Exocyst SEC3 and Phosphoinositides Define Sites of Exocytosis in Pollen Tube Initiation and Growth.","date":"2016","source":"Plant physiology","url":"https://pubmed.ncbi.nlm.nih.gov/27516531","citation_count":80,"is_preprint":false},{"pmid":"9826515","id":"PMC_9826515","title":"Isomorphous replacement of cystine with selenocystine in endothelin: oxidative refolding, biological and conformational properties of [Sec3,Sec11,Nle7]-endothelin-1.","date":"1998","source":"Journal of molecular 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Theoretische und angewandte Genetik","url":"https://pubmed.ncbi.nlm.nih.gov/24226219","citation_count":16,"is_preprint":false},{"pmid":"33973520","id":"PMC_33973520","title":"EXOC1 plays an integral role in spermatogonia pseudopod elongation and spermatocyte stable syncytium formation in mice.","date":"2021","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/33973520","citation_count":15,"is_preprint":false},{"pmid":"28765280","id":"PMC_28765280","title":"The exocyst subunit Sec3 is regulated by a protein quality control pathway.","date":"2017","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28765280","citation_count":12,"is_preprint":false},{"pmid":"9467657","id":"PMC_9467657","title":"Cytokine induction by Mycoplasma arthritidis-derived superantigen (MAS), but not by TSST-1 or SEC-3, is correlated to certain HLA-DR types.","date":"1998","source":"Scandinavian journal of 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cytoskeletons, and polarity establishment proteins, establishing it as a spatial landmark defining sites of exocytosis.\",\n      \"method\": \"GFP fusion live imaging, genetic epistasis with secretory and cytoskeletal mutants\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with functional consequence, replicated across multiple genetic backgrounds, foundational paper with 306 citations\",\n      \"pmids\": [\"9491896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Yeast SEC3 (ortholog of EXOC1) is required for targeting or fusion of post-Golgi secretory vesicles to the plasma membrane, genetically interacts with profilin (PFY1), and is required for correct bud site selection in diploids; high-copy SEC3 suppresses sec5-24.\",\n      \"method\": \"Genetic screen, synthetic lethality, gene dosage suppression, temperature-sensitive allele analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic methods, replicated in subsequent studies, 92 citations\",\n      \"pmids\": [\"9247645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In budding yeast, Sec3p (EXOC1 ortholog) and Exo70p remain stably associated with the plasma membrane independently of actin, while other exocyst subunits (Sec5p, Sec6p, Sec8p, Sec10p, Sec15p, Exo84p) are delivered on secretory vesicles; exocyst assembly occurs when vesicle-borne subunits join Sec3p/Exo70p at the plasma membrane.\",\n      \"method\": \"FRAP, immunogold electron microscopy, epifluorescence video microscopy, actin disruption experiments\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal imaging and biochemical methods, replicated, 241 citations\",\n      \"pmids\": [\"15583031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The N-terminus of yeast Sec3 (EXOC1 ortholog) directly interacts with phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) and with GTP-bound Cdc42; both interactions are required for Sec3 plasma membrane targeting, exocytosis, exocyst polarization, and normal cell morphogenesis.\",\n      \"method\": \"In vitro binding assays, site-directed mutagenesis of key residues, genetic analysis in yeast\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro binding with mutagenesis plus genetic validation, 206 citations\",\n      \"pmids\": [\"18195105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the yeast Sec3 N-terminal domain (EXOC1 ortholog) in complex with Rho1 at 2.6 Å reveals a pleckstrin homology (PH) fold; conserved basic residues form a PtdIns(4,5)P2-binding cleft, and residues Phe77, Ile115, Leu131 mediate binding to the hydrophobic surface around switch regions I and II of Rho1.\",\n      \"method\": \"X-ray crystallography, mutagenesis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation of interaction residues\",\n      \"pmids\": [\"20062059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The mammalian exocyst complex, including human Sec3 (EXOC1), interacts with RalA in a GTP-dependent manner in brain nerve terminals, identifying EXOC1 as a mammalian homologue of yeast Sec3p and placing the exocyst as an effector of RalA signaling in directing exocytosis sites.\",\n      \"method\": \"GTP-dependent affinity pulldown from brain lysates, MALDI-TOF MS identification, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal pulldown with MS identification in native brain tissue, single lab\",\n      \"pmids\": [\"11406615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human Sec3 (EXOC1) interacts with other exocyst subunits Sec5 and Sec8 in a yeast two-hybrid system; GFP-fusions of hSec3 are cytosolic in MDCK cells, and hSec3 lacks the Rho1-binding site present in yeast Sec3p.\",\n      \"method\": \"Yeast two-hybrid, GFP fusion expression in MDCK cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid plus cell imaging, single lab, partial mechanistic characterization\",\n      \"pmids\": [\"11493706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Yeast Sec3p (EXOC1 ortholog) is the only exocyst subunit capable of recruiting secretory vesicles when ectopically targeted to mitochondria, establishing Sec3p's unique role in vesicle tethering; Rab GTPase Sec4p and its GEF Sec2p regulate exocyst complex assembly.\",\n      \"method\": \"Ectopic mitochondrial targeting assay, epistasis analysis, fluorescence microscopy\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — novel reconstitution-like ectopic targeting assay with clear functional readout and multiple subunit comparisons\",\n      \"pmids\": [\"25232005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Yeast Sec3 (EXOC1 ortholog) directly interacts with the t-SNARE protein Sso2, promoting formation of the Sso2-Sec9 binary t-SNARE complex; crystal structure of the Sec3-Sso2 complex shows Sec3 binding induces conformational changes in Sso2 relieving its autoinhibition, thereby stimulating membrane fusion independently of vesicle tethering.\",\n      \"method\": \"Crystal structure, in vitro membrane fusion assay, site-directed mutagenesis, Co-IP\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with in vitro reconstituted membrane fusion assay and mutagenesis confirming functional separation from tethering\",\n      \"pmids\": [\"28112172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Mammalian Sec3 (EXOC1) associates with a subset of exocyst complexes enriched at desmosomes; RNAi-mediated Sec3 knockdown specifically impairs desmosome morphology and function without affecting adherens junctions; membrane recruitment of Sec3 depends on cadherin-mediated adhesion but occurs later than Sec6 and Sec8.\",\n      \"method\": \"RNAi knockdown, immunofluorescence, co-immunoprecipitation, functional junction assays in epithelial cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean RNAi KD with specific phenotypic readout and Co-IP, single lab\",\n      \"pmids\": [\"19889837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Human Sec3 (EXOC1) binds to the SH2 domain-binding motif of elongation factor 1α (EF1α) and sequesters it; this interaction suppresses flavivirus RNA transcription and translation. Flavivirus capsid protein (WNV/DENV C protein) binds to the first 15 amino acids of hSec3p to disrupt the hSec3p-EF1α complex.\",\n      \"method\": \"Yeast two-hybrid screen, mutagenesis, siRNA knockdown, viral replication assays\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — yeast two-hybrid plus mutagenesis with functional viral replication readout, single lab\",\n      \"pmids\": [\"19889084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"WNV and DENV capsid proteins interact physically with human Sec3 (EXOC1) and activate 20S proteasome chymotrypsin-like activity to degrade hSec3p post-transcriptionally; specific amino acids (14 of WNV C, 13 of DENV C) mediate C protein-hSec3p binding, and residues 109-114 (WNV) or 102-107 (DENV) constitute the degradation motif.\",\n      \"method\": \"Mutagenesis, co-immunoprecipitation, proteasome activity assays, siRNA knockdown\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mutagenesis plus binding and proteasome activity assays, single lab\",\n      \"pmids\": [\"23522008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Human/mouse Sec3 (EXOC1) physically interacts with the C-terminal tail of glycine transporter GLYT1 via pulldown and co-immunoprecipitation; coexpression with GLYT1 partially recruits Sec3-GFP to the plasma membrane; Sec3 increases GLYT1 transporter capacity, suggesting the exocyst promotes GLYT1 insertion into the plasma membrane.\",\n      \"method\": \"Yeast two-hybrid, pulldown, co-immunoprecipitation from rat brain, immunofluorescence, functional transport assay\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple binding methods plus functional transport assay, single lab\",\n      \"pmids\": [\"16181645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Homozygous knockout of mouse Exoc1 (EXOC1 ortholog) causes peri-implantation lethality, establishing an essential role for EXOC1 in early mouse development.\",\n      \"method\": \"Knockout mouse generation, genetic rescue analysis, expression analysis in blastocysts\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific lethal phenotype and genetic rescue experiment confirming Exoc1 as causative gene\",\n      \"pmids\": [\"26346620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EXOC1 promotes pseudopod formation in mouse spermatogonia by inactivating the Rho family GTPase Rac1, and functions in spermatocyte syncytia formation together with SNARE proteins STX2 and SNAP23.\",\n      \"method\": \"Conditional knockout mice, immunofluorescence, co-immunoprecipitation, Rac1 activity assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with specific cellular phenotype and co-IP identifying interacting partners, single lab\",\n      \"pmids\": [\"33973520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"EXOC1 depletion from mouse oocytes impairs intra-oocyte trafficking of c-KIT and GDF9, causing their abnormal cytoplasmic retention, leading to defective oocyte re-awakening, impaired cyst breakdown, and complete female infertility; phenotype is shared with depletion of exocyst members EXOC3 and EXOC7.\",\n      \"method\": \"Oocyte-specific conditional knockout, immunofluorescence localization of c-KIT and GDF9, fertility assays, comparison with EXOC3/EXOC7 KO\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with specific trafficking phenotype validated with multiple exocyst subunits, single lab\",\n      \"pmids\": [\"39833146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sec3 (EXOC1) knockdown in mouse hippocampal neurons prevents neuronal polarization and axon formation; in utero electroporation knockdown disrupts cortical neuron migration and morphology during neocortex formation.\",\n      \"method\": \"siRNA knockdown in primary hippocampal cultures, in utero electroporation, immunofluorescence\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with specific polarization and migration phenotypes in two independent neuronal systems\",\n      \"pmids\": [\"34862972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Sec3 (EXOC1) knockdown in A549 lung cancer cells abolishes TGF-β-stimulated cell migration and EMT, and specifically inhibits TGF-β-stimulated Akt phosphorylation without affecting Smad2 phosphorylation; these defects are rescued by RNAi-resistant Sec3.\",\n      \"method\": \"siRNA knockdown, rescue with RNAi-resistant construct, Western blot for pAkt/pSmad2, wound healing assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KD with rescue experiment and pathway-specific phosphorylation readout, single lab\",\n      \"pmids\": [\"31495494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Fission yeast Sec3 (EXOC1 ortholog) physically interacts with the formin For3; sec3 deletion causes loss of actin cables due to failure to polarize For3, and also disrupts actin patch polarity and actomyosin ring constriction/disassembly; human Sec3/EXOC1 rescues fission yeast sec3 mutants.\",\n      \"method\": \"Co-immunoprecipitation, FRAP, genetic deletion analysis, heterologous complementation with human EXOC1\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus genetic analysis plus human ortholog rescue confirming conservation, single lab\",\n      \"pmids\": [\"22891673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In Candida albicans, Sec3p (EXOC1 ortholog) is required for maintenance of hyphal tip growth after septin ring formation; the septin Cdc3p co-immunoprecipitates with Sec3p and Sec5p; deletion of septins Cdc10 or Cdc11 mislocalizes Sec3p and restores hyphal development in sec3Δ mutants, establishing a functional link between septins and exocyst-mediated polarized exocytosis.\",\n      \"method\": \"Co-immunoprecipitation, genetic deletion epistasis, fluorescence microscopy\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus genetic epistasis with clear phenotypic readout, single lab\",\n      \"pmids\": [\"17504812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In fission yeast, Sec3 (EXOC1 ortholog) degradation is regulated by the ubiquitin-proteasome system via the E3 ubiquitin ligase Pib1 and deubiquitylase Ubp3; blocking the proteasome or Hsp70-type chaperones suppresses sec3 mutant phenotypes including defects in exocytosis, endocytosis, and cell septation.\",\n      \"method\": \"Extragenic suppressor screen, proteasome inhibition, genetic analysis with E3 ligase and deubiquitylase mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — suppressor screen with multiple pathway components validated, single lab\",\n      \"pmids\": [\"28765280\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXOC1 (Sec3) is a subunit of the octameric exocyst complex that functions as both a spatial landmark and active regulator of polarized exocytosis: its PH-like N-terminal domain anchors it stably at the plasma membrane via direct binding to PtdIns(4,5)P2 and Rho-family GTPases (Cdc42/Rho1), it uniquely recruits secretory vesicles to tethering sites while other exocyst subunits arrive on vesicles, and it directly promotes SNARE complex assembly by binding t-SNARE Sso2 and relieving its autoinhibition to stimulate membrane fusion; in mammals, EXOC1 is essential for peri-implantation development, spermatogenesis (via Rac1 inactivation and SNARE interactions), oocyte trafficking of c-KIT and GDF9, desmosome assembly, neuronal polarization, and TGF-β/Akt-dependent cell migration.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EXOC1 (Sec3) is a subunit of the octameric exocyst complex that serves as a spatial landmark for polarized exocytosis and actively promotes membrane fusion. In yeast, Sec3 localizes to exocytic sites independently of the secretory pathway and actin cytoskeleton, where its PH-domain N-terminus binds PtdIns(4,5)P2 and Rho-family GTPases (Cdc42, Rho1) to anchor the complex at the plasma membrane, and it is the only exocyst subunit capable of recruiting secretory vesicles when ectopically targeted [PMID:9491896, PMID:18195105, PMID:20062059, PMID:25232005]. Sec3 also directly binds the t-SNARE Sso2, relieving its autoinhibition to stimulate SNARE complex assembly and membrane fusion independently of its tethering function [PMID:28112172]. In mammals, EXOC1 is essential for peri-implantation development, and conditional loss-of-function studies demonstrate requirements in spermatogenesis via Rac1 inactivation and SNARE interactions, oocyte trafficking of c-KIT and GDF9, desmosome assembly, neuronal polarization, and TGF-β/Akt-dependent cell migration [PMID:26346620, PMID:33973520, PMID:39833146, PMID:19889837, PMID:34862972, PMID:31495494].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"The initial question was whether Sec3 functions in exocytosis; genetic analysis established that SEC3 is required for post-Golgi vesicle targeting or fusion at the plasma membrane and genetically interacts with cytoskeletal regulators.\",\n      \"evidence\": \"Temperature-sensitive alleles, synthetic lethality with profilin, gene dosage suppression in budding yeast\",\n      \"pmids\": [\"9247645\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No biochemical mechanism identified\", \"No distinction between tethering and fusion roles\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"A central question was how exocytic sites are spatially specified; live imaging revealed that Sec3p localizes to polarized growth sites independently of the secretory pathway, actin, and septins, establishing it as a unique spatial landmark among exocyst subunits.\",\n      \"evidence\": \"GFP-Sec3 imaging across multiple yeast secretory and cytoskeletal mutants\",\n      \"pmids\": [\"9491896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of membrane targeting unknown\", \"Whether mammalian EXOC1 behaves identically unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The mammalian EXOC1 ortholog was identified as a component of the exocyst complex in brain, linking it to RalA GTPase signaling, and initial characterization showed human Sec3 differs from yeast Sec3 in lacking the Rho1-binding site and displaying cytosolic localization in epithelial cells.\",\n      \"evidence\": \"GTP-dependent pulldown with MALDI-TOF MS from rat brain; yeast two-hybrid with exocyst subunits; GFP imaging in MDCK cells\",\n      \"pmids\": [\"11406615\", \"11493706\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian membrane targeting mechanism unresolved\", \"Functional role of mammalian EXOC1 not yet tested by loss-of-function\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The question of how the exocyst assembles was addressed by showing Sec3p and Exo70p remain stably at the plasma membrane while six other subunits arrive on secretory vesicles, defining a two-pool assembly model.\",\n      \"evidence\": \"FRAP, immunogold EM, and video microscopy with actin disruption in budding yeast\",\n      \"pmids\": [\"15583031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of subunit-subunit assembly not resolved\", \"Whether this model applies in mammalian cells unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The molecular basis of Sec3 membrane anchoring was resolved: the N-terminus directly binds PtdIns(4,5)P2 and GTP-Cdc42, and both interactions are required for polarized localization and exocytosis.\",\n      \"evidence\": \"In vitro lipid/GTPase binding assays with point mutagenesis and genetic validation in yeast\",\n      \"pmids\": [\"18195105\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic details of dual-lipid/GTPase recognition not yet available\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Structural determination of the Sec3 N-terminal domain in complex with Rho1 revealed a PH fold with a PtdIns(4,5)P2-binding basic cleft and a hydrophobic interface for Rho GTPase recognition, providing the atomic framework for membrane targeting.\",\n      \"evidence\": \"2.6 Å crystal structure with mutagenesis validation\",\n      \"pmids\": [\"20062059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length Sec3 structure not determined\", \"No structure of the mammalian EXOC1 domain\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Sec3 was linked to septin-dependent polarity control: in C. albicans, Sec3p co-immunoprecipitates with septins and is required for hyphal tip growth after septin ring formation, with septin deletion epistatic to sec3Δ.\",\n      \"evidence\": \"Co-IP and genetic epistasis with fluorescence microscopy in C. albicans\",\n      \"pmids\": [\"17504812\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect septin–Sec3 interaction not distinguished\", \"Relevance to mammalian septins untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mammalian EXOC1 was found to have a specific role in desmosome assembly: Sec3 knockdown impairs desmosome but not adherens junction integrity, and Sec3 is recruited to cell–cell contacts in a cadherin-dependent manner.\",\n      \"evidence\": \"RNAi, co-IP, and functional junction assays in epithelial cells\",\n      \"pmids\": [\"19889837\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cargo delivered by EXOC1-containing exocyst to desmosomes not identified\", \"Whether EXOC1 acts as a full-complex subunit or sub-complex at desmosomes unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Sec3 was shown to physically interact with the formin For3 in fission yeast and is required for actin cable polarization; human EXOC1 rescues fission yeast sec3 mutants, demonstrating functional conservation.\",\n      \"evidence\": \"Co-IP, FRAP, genetic deletion, and heterologous complementation\",\n      \"pmids\": [\"22891673\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface between Sec3 and formin not mapped\", \"Whether EXOC1 regulates mammalian formins untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Among all eight exocyst subunits, only Sec3 can recruit secretory vesicles when ectopically targeted to mitochondria, resolving the question of which subunit initiates vesicle tethering.\",\n      \"evidence\": \"Ectopic mitochondrial targeting assay with fluorescence microscopy in yeast\",\n      \"pmids\": [\"25232005\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of Sec3's unique vesicle-recruiting capability not identified\", \"Whether this applies in mammalian cells unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Homozygous Exoc1 knockout in mice causes peri-implantation lethality, establishing EXOC1 as essential for early mammalian development.\",\n      \"evidence\": \"Constitutive knockout mouse with genetic rescue\",\n      \"pmids\": [\"26346620\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific developmental process requiring EXOC1 at peri-implantation not identified\", \"Cell-type-specific requirements not dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Sec3 was shown to directly promote SNARE-mediated membrane fusion by binding t-SNARE Sso2 and relieving its autoinhibition, establishing a fusion-promoting function mechanistically separable from vesicle tethering.\",\n      \"evidence\": \"Crystal structure of Sec3–Sso2 complex, in vitro reconstituted membrane fusion assay, mutagenesis\",\n      \"pmids\": [\"28112172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian EXOC1 similarly activates cognate t-SNAREs not tested\", \"Integration of tethering and fusion-promoting activities in vivo not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Sec3 protein turnover was found to be regulated by the ubiquitin-proteasome system via E3 ligase Pib1 and deubiquitylase Ubp3, connecting protein quality control to exocyst function.\",\n      \"evidence\": \"Extragenic suppressor screen with proteasome inhibition and genetic analysis in fission yeast\",\n      \"pmids\": [\"28765280\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitylation sites on Sec3 not mapped\", \"Whether mammalian EXOC1 turnover is similarly regulated unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"EXOC1 was placed in TGF-β signaling: Sec3 knockdown abolishes TGF-β-stimulated Akt phosphorylation and cell migration without affecting Smad2 signaling, identifying EXOC1 as a pathway-selective mediator of non-canonical TGF-β signaling.\",\n      \"evidence\": \"siRNA knockdown with RNAi-resistant rescue, Western blot, wound healing assay in A549 cells\",\n      \"pmids\": [\"31495494\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which EXOC1 selectively modulates Akt signaling unknown\", \"Only tested in one cancer cell line\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Conditional knockout studies established EXOC1 as essential for spermatogenesis, where it promotes pseudopod formation via Rac1 inactivation and spermatocyte syncytia formation through interaction with SNARE proteins STX2 and SNAP23, and for neuronal polarization and cortical migration.\",\n      \"evidence\": \"Conditional knockout mice with Rac1 activity assays and co-IP (spermatogenesis); siRNA and in utero electroporation (neurons)\",\n      \"pmids\": [\"33973520\", \"34862972\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether EXOC1 directly inhibits Rac1 or acts through a GAP not determined\", \"Cargo delivered during neuronal polarization not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"EXOC1 depletion from oocytes impairs intra-oocyte trafficking of c-KIT and GDF9, causing their cytoplasmic retention and leading to defective cyst breakdown and female infertility, extending the mammalian EXOC1 requirement to oogenesis.\",\n      \"evidence\": \"Oocyte-specific conditional knockout with immunofluorescence and fertility assays in mice\",\n      \"pmids\": [\"39833146\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether EXOC1 directly traffics c-KIT/GDF9 or acts indirectly through general exocytic machinery unclear\", \"Single lab finding\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the structure of full-length mammalian EXOC1, whether mammalian EXOC1 directly activates cognate t-SNAREs as yeast Sec3 does, the identity of specific cargo delivered by EXOC1-containing exocyst subcomplexes in different mammalian cell types, and the mechanism by which EXOC1 selectively modulates non-canonical TGF-β/Akt signaling.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length mammalian EXOC1 structure\", \"No in vitro reconstitution of mammalian EXOC1-SNARE activation\", \"Cargo specificity in distinct mammalian tissues unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 3, 4]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 2, 7, 8]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [12, 15]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 17]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [13, 14, 16]}\n    ],\n    \"complexes\": [\n      \"exocyst complex\"\n    ],\n    \"partners\": [\n      \"EXOC2\",\n      \"EXOC3\",\n      \"STX2\",\n      \"SNAP23\",\n      \"RALA\",\n      \"CDC42\",\n      \"RAC1\",\n      \"EEF1A1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}