{"gene":"STN1","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1997,"finding":"Yeast Stn1 physically interacts with Cdc13 (by two-hybrid analysis) and functions in telomere length regulation; loss of Stn1 function causes accumulation of single-stranded DNA in subtelomeric regions and activates the RAD9/MEC3 G2/M DNA damage checkpoints.","method":"Two-hybrid interaction, genetic suppressor screen, ssDNA detection assay, checkpoint genetic analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic and physical interaction data, replicated across multiple labs in subsequent work","pmids":["9042864"],"is_preprint":false},{"year":2000,"finding":"Stn1 acts as an inhibitor of telomerase recruitment by Cdc13; a Cdc13-Stn1 fusion protein blocks telomere elongation, indicating Stn1 negatively regulates the telomerase-loading function of Cdc13.","method":"Fusion protein overexpression, telomere length assays, genetic epistasis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fusion protein and genetic experiments in single lab, two complementary approaches","pmids":["11046137"],"is_preprint":false},{"year":2001,"finding":"Ten1 physically associates with both Stn1 and Cdc13; a binding defect between Stn1-13 and Ten1 underlies the long-telomere phenotype; Ten1 is required for telomere length regulation and preventing single-stranded DNA accumulation at telomeres.","method":"Two-hybrid interaction, genetic complementation, ssDNA assay, checkpoint analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal physical interaction, allele-specific genetic rescue, replicated by subsequent structural studies","pmids":["11230140"],"is_preprint":false},{"year":2007,"finding":"Fission yeast Stn1 and Ten1 are essential for chromosome end protection and form a complex with each other but not with Pot1; they localize at telomeres in a manner correlated with ssDNA overhang length, and both contain OB-fold domains.","method":"Genetic deletion, co-immunoprecipitation, telomere localization assay, structural bioinformatics","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function genetics plus direct localization and protein interaction experiments, replicated across species","pmids":["17715303"],"is_preprint":false},{"year":2008,"finding":"Stn1 has two separable functional domains: the N-terminus interacts with Ten1 and is essential for telomere capping, while the C-terminus binds both Cdc13 and Pol12 and is required to limit continuous telomerase action. Stn1 telomere association peaks in S phase.","method":"Domain dissection/truncation analysis, genetic complementation, chromatin immunoprecipitation, in vivo binding assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple domain mutants, orthogonal genetic and ChIP assays, two separable phenotypes established","pmids":["19172739"],"is_preprint":false},{"year":2009,"finding":"Mammalian STN1 and TEN1 homologs were identified and shown to form the CST (CTC1-STN1-TEN1) complex that binds single-stranded DNA with high affinity in a sequence-independent manner; knockdown of Stn1 causes significant increases in single-stranded G-strand telomeric DNA.","method":"Protein identification, co-immunoprecipitation, ssDNA-binding assay, siRNA knockdown, telomere ssDNA quantification","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical complex reconstitution, binding assay, functional knockdown with defined telomeric phenotype","pmids":["19854130"],"is_preprint":false},{"year":2009,"finding":"Human OBFC1 (STN1) associates with TPP1 in the telomere interactome, localizes to telomeres in human cells, binds telomeric single-stranded DNA in vitro, and overexpression of an OBFC1 mutant results in telomere elongation.","method":"Proteomic co-immunoprecipitation, telomere localization (FISH/immunofluorescence), in vitro DNA binding assay, overexpression telomere length assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulldown plus localization plus in vitro binding, single lab","pmids":["19648609"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the Candida tropicalis Stn1N-Ten1 complex shows an RPA2N-RPA3-like architecture with OB-fold packing; the C-terminal domain of S. cerevisiae Stn1 contains two WH motifs similar to RPA2-C. Mutations disrupting Stn1-Ten1 interaction cause telomere uncapping and abolish Ten1 telomere localization.","method":"X-ray crystallography, mutational analysis, telomere localization assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures from multiple species plus functional mutagenesis validation","pmids":["20008938"],"is_preprint":false},{"year":2009,"finding":"AtCTC1 (plant CTC1) physically and genetically interacts with AtSTN1; both are required for telomere integrity in Arabidopsis. Human CTC1 depletion by RNAi triggers DNA damage response and telomere defects, demonstrating conservation of the CST complex.","method":"Co-immunoprecipitation, genetic interaction, RNAi knockdown, telomere analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — physical and genetic interaction corroborated across plant and human systems, independent of PMID:19854130","pmids":["19854131"],"is_preprint":false},{"year":2009,"finding":"Overproduction of yeast Stn1 blocks S-phase checkpoint functions downstream of Rad53 activation; Stn1 broadly associates with chromosomes and its checkpoint-overriding effect depends on Pol12 (a subunit of DNA Pol α), indicating Stn1 promotes Pol α activity genome-wide when overproduced.","method":"Overexpression analysis, checkpoint kinase activation assay, chromatin binding assay, pol12 genetic rescue","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with pol12 plus chromatin binding, single lab","pmids":["19171895"],"is_preprint":false},{"year":2010,"finding":"Structural prediction and mutagenesis of a predicted alpha-helix in the N-terminal OB fold of S. cerevisiae Stn1 identified a specific Stn1-Ten1 interaction interface; stn1-L164D eliminates Ten1 association and is specifically suppressed by ten1-D138Y, confirming the interface.","method":"Structure-based mutagenesis, two-hybrid interaction, allele-specific suppression genetics","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — allele-specific suppression (strong genetic evidence) plus binding assay, single lab","pmids":["20157006"],"is_preprint":false},{"year":2011,"finding":"Xenopus CST (xCST) is involved in priming DNA synthesis on ssDNA templates in egg extracts; immunodepletion of xStn1 does not impair replication of chromatin DNA but specifically blocks the priming step on ssDNA templates, consistent with a role in telomeric C-strand synthesis regulation of Pol α-primase.","method":"Xenopus egg extract reconstitution, immunodepletion, in vitro DNA synthesis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with immunodepletion, primed vs. unprimed substrate comparison, single lab","pmids":["22086929"],"is_preprint":false},{"year":2012,"finding":"Human Stn1 depletion causes catastrophic telomere shortening and DNA damage specifically at lagging-strand telomeres; hStn1 promotes efficient replication of lagging-strand telomeric DNA, and its loss leads to persistent/elevated association of DNA Pol α with telomeres, suggesting hStn1 modulates Pol α synthesis activity rather than controlling its loading.","method":"shRNA knockdown, BrdU incorporation/FISH, telomere fragility assay, ChIP for Pol α","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with multiple orthogonal readouts, strand-specific phenotype established, reproduced in subsequent studies","pmids":["22964711"],"is_preprint":false},{"year":2012,"finding":"Cdc13 OB2 domain forms a homodimer; disruption of OB2 dimerization (e.g., by cdc13-1 mutation) impairs Cdc13-Stn1 association and causes telomere length deregulation, establishing that Cdc13 OB2 dimerization is required for proper CST assembly and productive telomere capping.","method":"X-ray crystallography, biochemical binding assay, in vivo telomere length assay, mutagenesis","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biochemical validation and in vivo functional assay, single lab","pmids":["23177925"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of the human STN1-TEN1 complex reveals hSTN1 with an OB domain and tandem C-terminal wHTH motifs, and hTEN1 with a single OB fold; the complex is structurally similar to RPA. hSTN1 is primarily responsible for ssDNA binding; cells expressing hSTN1 dimerization-defective mutants show elongated telomeres and telomere uncapping defects, indicating hTEN1 is required for hCST telomeric function.","method":"X-ray crystallography, in vitro ssDNA binding assay, cell-based telomere length and damage assay, mutagenesis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis plus functional cell-based assays","pmids":["23826127"],"is_preprint":false},{"year":2013,"finding":"Cdk1 phosphorylates Stn1 at threonine 223 and serine 250 in vitro and in vivo; these phosphorylations are essential for stability of CST complexes at telomeres and regulate the temporal recruitment of CST versus telomerase complexes during the cell cycle.","method":"In vitro kinase assay, phospho-site mutagenesis, chromatin immunoprecipitation, telomere length assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation confirmed in vivo, phospho-mutants tested for CST telomere association, single lab","pmids":["24164896"],"is_preprint":false},{"year":2014,"finding":"Purified CST from Candida glabrata substantially augments primase activity and primase-to-polymerase switching of the primase-Pol α (PP) complex; CST shortens RNA and lengthens DNA in chimeric products. Stn1 alone is sufficient for PP stimulation, acting through both its N-terminal OB fold and C-terminal WH domains via direct binding to the Pol12 subunit of PP.","method":"In vitro biochemical reconstitution with purified complexes, primase assay, primase-to-polymerase switch assay, binding assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — fully reconstituted in vitro system with purified components, domain dissection, mechanism defined","pmids":["25503194"],"is_preprint":false},{"year":2014,"finding":"SUMOylation of fission yeast shelterin subunit Tpz1 (TPP1 ortholog) on lysine 242 promotes recruitment of Stn1-Ten1 to telomeres and prevents telomerase accumulation, establishing a SUMO-dependent pathway that links shelterin to CST-mediated telomerase inhibition.","method":"SUMOylation site mutagenesis, telomere ChIP for Stn1 and telomerase, telomere length assay, SUMO-fusion protein binding assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — site-specific mutagenesis plus ChIP plus SUMO-fusion binding assay, independently confirmed in separate study (PMID:24925530)","pmids":["24711392"],"is_preprint":false},{"year":2014,"finding":"Fission yeast Tpz1 (TPP1 ortholog) SUMOylation promotes Stn1 telomere association via direct increased affinity of SUMO-Tpz1 for Stn1, independently confirmed and showing evolutionary conservation of SUMO-dependent CST recruitment.","method":"Protein interaction assay (SUMO-fusion pulldown), telomere ChIP, telomere length assay","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding assay plus ChIP, replicates PMID:24711392 finding with orthogonal approach","pmids":["24925530"],"is_preprint":false},{"year":2014,"finding":"Stn1 and Ten1 can function in a Cdc13-independent manner; disabling NMD alters CST stoichiometry at telomeres and permits Stn1 to bind telomeres without Cdc13, establishing Stn1 and Ten1 as the essential core of the CST capping complex.","method":"Genetic epistasis (NMD/DDR pathway mutations), ChIP for Stn1, telomere ssDNA assay","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis plus ChIP, single lab, mechanistic conclusion supported by two approaches","pmids":["24835988"],"is_preprint":false},{"year":2016,"finding":"An OB-fold mutation in STN1 (STN1-OBM) preferentially destabilizes binding to short ssDNA substrates and selectively impairs resolution of endogenous replication stress and telomere duplex replication in vivo, but does not affect telomeric C-strand fill-in or origin firing after exogenous replication stress, indicating mechanistic differences in CST action at different replication problems.","method":"In vitro ssDNA binding assay, STN1 mutant cell-based phenotypic analysis, telomere replication assay","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro binding combined with multiple in vivo functional assays, separation-of-function mutant","pmids":["27690379"],"is_preprint":false},{"year":2017,"finding":"Human STN1 alone (purified) stimulates primase-Pol α (PP) activity in vitro primarily through its N-terminal OB fold by binding POLA2; the STN1-POLA2 interaction targets the central OB fold domain of POLA2, which in the substrate-free PP structure blocks nucleic acid entry to the Pol α active site. A disease-causing STN1 mutation selectively disrupts POLA2 binding and PP stimulation.","method":"In vitro PP stimulation assay with purified proteins, pull-down binding assay, disease mutant analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro biochemical assay, domain mapping, disease mutation validates functional relevance","pmids":["28934486"],"is_preprint":false},{"year":2018,"finding":"CTC1-STN1 together limits telomerase action to prevent G-overhang overextension; TEN1 is separately essential for C-strand synthesis. CTC1-STN1 retains ssDNA affinity without TEN1 but TEN1 stabilizes binding; CTC1-STN1 binding to DNA Pol α is required to fully repress telomerase activity.","method":"CRISPR/Cas9 knockout of individual CST subunits, telomere overhang analysis, telomerase recruitment ChIP, in vitro DNA binding assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic dissection of individual subunit contributions, multiple orthogonal readouts, corroborated in PMID:29774655","pmids":["30026550"],"is_preprint":false},{"year":2018,"finding":"CRISPR-engineered CTC1-L1142H (Coats plus mutation) disrupts CTC1-STN1 interaction, leading to telomerase-mediated telomere elongation; impaired CTC1:STN1-DNA Pol α binding further de-represses telomerase; CP CTC1 mutants failing to interact with Pol α cause loss of C-strand maintenance and catastrophic telomere shortening.","method":"CRISPR/Cas9 knock-in, co-immunoprecipitation, telomere length assay, telomerase recruitment ChIP, Pol α interaction assay","journal":"Aging cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous knock-in mutation with multiple functional assays, consistent with PMID:30026550","pmids":["29774655"],"is_preprint":false},{"year":2018,"finding":"Fission yeast Stn1 contains a SUMO-interacting motif (SIM) in its C-terminal domain that is required for interaction with SUMO and SUMO-Tpz1; SIM point mutations (Stn1-226) cause telomere elongation, impair Stn1-Ten1 recruitment to telomeres, and enhance telomerase binding, establishing the SIM as critical for telomerase inhibition at chromosome ends.","method":"SIM mutagenesis, SUMO interaction assay, telomere ChIP, telomere length assay, telomerase ChIP","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — point mutations in defined motif, multiple orthogonal assays (binding, ChIP, length), consistent with independent SUMO pathway studies","pmids":["29774234"],"is_preprint":false},{"year":2021,"finding":"The intrinsically disordered region (IDR) within the STN1 OB-fold domain is critical for maintaining genome stability under replication stress; single IDR mutations cause genome instability and reduced viability, reduce RAD51 foci under replication stress, and impair STN1-POL α interaction, without affecting CST complex formation or STN1-RAD51 direct binding.","method":"Site-directed mutagenesis, cell viability assay, RAD51 foci immunofluorescence, co-immunoprecipitation, HU sensitivity assay","journal":"Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with multiple cellular phenotype readouts, single lab","pmids":["34681076"],"is_preprint":false},{"year":2022,"finding":"Yeast Stn1 overproduction circumvents Rad53 S-phase checkpoint through the MCM complex; Mcm2/Mcm5 mutations block Stn1-overproduction checkpoint bypass, loss-of-function stn1 mutations compensate rad53 defects, and Stn1 overproduction suppresses mcm7 mutants, indicating Stn1 functions as an accessory replication factor facilitating MCM activation at origins.","method":"Genetic epistasis, suppressor analysis, origin firing assay, ssDNA accumulation assay","journal":"Current genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple MCM alleles, single lab","pmids":["35150303"],"is_preprint":false},{"year":2023,"finding":"STN1 is phosphorylated by both ATR-CHK1 and CaMKK2 in its intrinsically disordered region in response to replication stress (hydroxyurea/aphidicolin or elevated cytosolic calcium); loss of STN1 phosphorylation reduces STN1 localization to stalled forks, elevates nascent strand degradation, increases MRE11 access, and decreases RAD51 at forks.","method":"In vitro kinase assay, phospho-site mutagenesis, fork protection assay (iPOND/fiber), MRE11/RAD51 ChIP at forks","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay validated in vivo, phospho-mutant functional analysis with multiple orthogonal readouts","pmids":["38036565"],"is_preprint":false},{"year":2023,"finding":"STN1 deficiency down-regulates multiple DNA glycosylases, resulting in defective base excision repair (BER) and accumulation of oxidative DNA damage, identifying a STN1-BER axis that protects colon tissue.","method":"Conditional STN1 knockout mouse model, BER activity assay, DNA glycosylase expression analysis, oxidative damage quantification","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo conditional KO with defined BER mechanistic readout, single lab","pmids":["37163605"],"is_preprint":false},{"year":2025,"finding":"The CST complex suppresses DNA end resection by EXO1 and the BLM-DNA2 helicase-nuclease complex via distinct mechanisms; BRCA1-BARD1 alleviates the CST-imposed EXO1 blockade but has little effect on BLM-DNA2 restriction. CST mutants impaired for DNA binding or BLM-EXO1 interaction exhibit hyper-resection and render BRCA1-deficient cells resistant to PARP inhibitors.","method":"Biochemical resection assay, CST DNA-binding and protein-interaction mutant analysis, cell-based PARPi resistance assay","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution of resection suppression, mechanistic mutant separation, functional cell-based validation","pmids":["40403056"],"is_preprint":false},{"year":2025,"finding":"STN1 directly interacts with the transcription factor STAT3 and structurally displaced ssDNA flanking R-loops at gene promoters, recruiting STAT3 to activate ZEB1 transcription independently of its telomere maintenance function, thereby promoting EMT and metastasis in pancreatic cancer.","method":"Co-immunoprecipitation, ChIP, R-loop detection, ZEB1 reporter assay, STAT3 inhibitor rescue","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and ChIP in multiple PDAC models, single lab, non-telomeric function","pmids":["40841373"],"is_preprint":false},{"year":2025,"finding":"STN1 directly interacts with CTC1 at the OB-G domain and competes with TRIM32 for the same binding region; STN1 binding prevents TRIM32-mediated ubiquitination and proteasomal degradation of CTC1, thereby stabilizing the CST complex.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor rescue, structural modeling (AlphaFold3)","journal":"Aging cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and ubiquitination assay, single lab, structural model supporting but not definitively confirming binding interface","pmids":["40923710"],"is_preprint":false},{"year":2025,"finding":"STN1 interacts with ATM and stabilizes ATM expression and signaling after DNA damage; STN1 silencing reduces both homologous recombination and non-homologous end joining repair of DSBs and impairs G2/M checkpoint arrest after ionizing radiation, in a CST complex-independent manner.","method":"Co-immunoprecipitation/proteomic interaction screen, ATM expression/signaling assay, HR/NHEJ reporter assay, cell cycle checkpoint assay after IR","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomic interaction plus functional DSB repair assays, single lab","pmids":["41036624"],"is_preprint":false},{"year":2025,"finding":"Conditional deletion of human STN1 causes proliferation defects, telomeric damage signaling, G-overhang overextension, and genome instability (anaphase bridges, micronuclei); these phenotypes are largely dependent on telomerase activity, establishing that STN1 limits telomerase-mediated G-overhang extension.","method":"Conditional CRISPR/Cas9 knockout, telomere overhang assay, telomere damage focus quantification, telomerase inhibition rescue","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple phenotypic readouts and genetic rescue by telomerase inhibition","pmids":["42148867"],"is_preprint":false},{"year":2026,"finding":"In zebrafish, Stn1 interacts with the transcription factor Tcf/Lef, facilitates its association with promoters of germ cell-specific genes, and enhances Wnt/β-catenin signaling activity in oocytes; genetic deletion of stn1 leads to massive oocyte loss.","method":"Co-immunoprecipitation, ChIP at germ cell promoters, conditional genetic knockout, Wnt pathway reporter assay","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and ChIP plus genetic KO with phenotypic rescue, single organism/lab","pmids":["41998405"],"is_preprint":false}],"current_model":"STN1 (OBFC1) is a core subunit of the RPA-like CST (CTC1-STN1-TEN1) heterotrimeric complex that binds single-stranded DNA via OB-fold domains; its N-terminal OB fold and intrinsically disordered region support ssDNA binding, Pol α-primase stimulation (by direct interaction with POLA2/Pol12), and fork protection, while its C-terminal winged-helix domain interacts with Cdc13/CTC1 and Ten1 to assemble the CST complex; at telomeres, CTC1-STN1 terminates telomerase-mediated G-overhang extension and—together with TEN1—promotes C-strand fill-in by DNA Pol α-primase; STN1 phosphorylation by ATR-CHK1 and CaMKK2 enables its recruitment to stalled replication forks where it blocks MRE11-mediated nascent strand degradation; CST additionally suppresses DSB end resection by EXO1 and BLM-DNA2 to direct break repair pathway choice; STN1 also stabilizes CTC1 by competing with the E3 ubiquitin ligase TRIM32, and harbors non-telomeric functions including regulation of base excision repair, ATM-dependent DSB repair, and transcriptional activation via R-loop-associated ssDNA binding."},"narrative":{"mechanistic_narrative":"STN1 is a core subunit of the conserved RPA-like CST (CTC1–STN1–TEN1) complex that binds single-stranded DNA via OB-fold domains and governs telomere end protection and genome-wide replication [PMID:19854130, PMID:23826127]. It was first defined in budding yeast through physical and genetic interaction with Cdc13, where loss of Stn1 causes subtelomeric ssDNA accumulation and checkpoint activation [PMID:9042864], and through its negative regulation of Cdc13-mediated telomerase recruitment [PMID:11046137]. STN1 partitions into separable modules: its N-terminal OB fold heterodimerizes with TEN1 in an RPA2N–RPA3-like architecture essential for telomere capping, while its C-terminal tandem winged-helix domains engage Cdc13/CTC1 and the Pol12/POLA2 subunit of DNA polymerase α-primase to limit telomerase action [PMID:19172739, PMID:20008938, PMID:23826127]. At chromosome ends CTC1–STN1 terminates telomerase-mediated G-overhang extension while TEN1-assisted CST promotes C-strand fill-in by stimulating the priming and primase-to-polymerase switch of Pol α-primase through direct binding to POLA2, a stimulation STN1 can drive on its own [PMID:25503194, PMID:28934486, PMID:30026550, PMID:42148867]. Beyond telomeres, STN1 is recruited to stalled replication forks following ATR–CHK1 and CaMKK2 phosphorylation of its intrinsically disordered region, where it blocks MRE11-mediated nascent-strand degradation and maintains RAD51 [PMID:34681076, PMID:38036565], and CST suppresses DSB end resection by EXO1 and BLM–DNA2 to influence repair-pathway choice and PARP-inhibitor sensitivity [PMID:40403056]. STN1 additionally stabilizes CTC1 by competing with the E3 ligase TRIM32 [PMID:40923710] and carries CST-independent roles spanning base excision repair, ATM-dependent DSB repair, and R-loop-associated transcriptional activation via STAT3 and Tcf/Lef [PMID:37163605, PMID:40841373, PMID:41036624, PMID:41998405]. A disease-causing STN1 mutation that selectively disrupts POLA2 binding links the Pol α-stimulating function to Coats plus–spectrum telomere pathology [PMID:28934486, PMID:29774655].","teleology":[{"year":1997,"claim":"Established Stn1 as a telomere-associated factor by showing it binds Cdc13 and that its loss produces subtelomeric ssDNA and checkpoint activation, defining a capping rather than length-only function.","evidence":"Two-hybrid interaction, genetic suppressor screen, ssDNA detection and checkpoint analysis in budding yeast","pmids":["9042864"],"confidence":"High","gaps":["Molecular basis of Cdc13–Stn1 binding undefined","No biochemical demonstration of ssDNA binding by Stn1 itself"]},{"year":2000,"claim":"Resolved whether Stn1 promotes or restrains telomerase, showing it is a negative regulator of Cdc13-dependent telomerase loading.","evidence":"Cdc13-Stn1 fusion overexpression and telomere length/epistasis assays in yeast","pmids":["11046137"],"confidence":"Medium","gaps":["Fusion protein may not reflect endogenous regulation","Mechanism of telomerase exclusion not defined"]},{"year":2001,"claim":"Identified Ten1 as the third partner, establishing a three-component capping module and that Stn1–Ten1 contacts are required to restrain telomere length.","evidence":"Two-hybrid, allele-specific genetic rescue, ssDNA and checkpoint assays in yeast","pmids":["11230140"],"confidence":"High","gaps":["Stoichiometry and structure of the trimer unknown","Direct DNA-binding role of each subunit unresolved"]},{"year":2007,"claim":"Showed conservation in fission yeast and that Stn1–Ten1 form an OB-fold complex independent of Pot1, positioning CST as a distinct end-protection entity.","evidence":"Gene deletion, co-IP, telomere localization and structural bioinformatics in fission yeast","pmids":["17715303"],"confidence":"High","gaps":["OB-fold predictions not yet structurally confirmed","Relationship to Pol α not addressed"]},{"year":2008,"claim":"Mapped Stn1 into separable N-terminal (Ten1/capping) and C-terminal (Cdc13/Pol12/telomerase-limiting) functional domains, dissecting its dual roles.","evidence":"Truncation/domain mutagenesis, genetic complementation and ChIP in yeast","pmids":["19172739"],"confidence":"High","gaps":["Structural interfaces unresolved","How Pol12 binding limits telomerase mechanistically unclear"]},{"year":2009,"claim":"Extended CST to mammals and plants, defining the human CTC1–STN1–TEN1 complex as a high-affinity sequence-independent ssDNA binder whose loss elevates telomeric G-strand ssDNA.","evidence":"Complex purification, co-IP, ssDNA-binding, siRNA/RNAi knockdown, telomere interactome proteomics across human, plant and yeast","pmids":["19854130","19648609","19854131"],"confidence":"High","gaps":["Which subunit carries primary DNA-binding activity not yet assigned","Telomerase-regulation mechanism in human cells undefined"]},{"year":2009,"claim":"Linked Stn1 to genome-wide Pol α activity by showing its overproduction overrides the S-phase checkpoint in a Pol12-dependent manner.","evidence":"Overexpression, Rad53 activation assay, chromatin binding and pol12 genetic rescue in yeast","pmids":["19171895"],"confidence":"Medium","gaps":["Overexpression phenotype may not mirror physiological role","Direct effect on Pol α biochemistry not shown"]},{"year":2009,"claim":"Provided the first structural framework, showing Stn1N–Ten1 adopts an RPA2N–RPA3-like fold and that disrupting this interface causes uncapping.","evidence":"X-ray crystallography of Candida Stn1N–Ten1 plus mutational telomere localization assays","pmids":["20008938"],"confidence":"High","gaps":["Full-length trimer structure unsolved","C-terminal WH domain functions not structurally defined"]},{"year":2010,"claim":"Refined the Stn1–Ten1 interface to a specific N-terminal helix via allele-specific suppression, validating the structural model genetically.","evidence":"Structure-based mutagenesis, two-hybrid and allele-specific suppression in yeast","pmids":["20157006"],"confidence":"Medium","gaps":["Single-lab genetic data","Interface conservation in human STN1 not tested here"]},{"year":2011,"claim":"Demonstrated that vertebrate CST specifically supports priming of DNA synthesis on ssDNA templates, connecting Stn1 directly to Pol α-primase function.","evidence":"Xenopus egg extract reconstitution with xStn1 immunodepletion and in vitro DNA synthesis assays","pmids":["22086929"],"confidence":"High","gaps":["Direct Pol α-binding partner not yet identified","Telomere specificity vs general priming unresolved"]},{"year":2012,"claim":"Established that human STN1 is required for efficient lagging-strand telomere replication and modulates Pol α synthesis rather than its loading.","evidence":"shRNA knockdown, BrdU/FISH, telomere fragility and Pol α ChIP in human cells","pmids":["22964711"],"confidence":"High","gaps":["Mechanism by which STN1 modulates Pol α activity unresolved","Distinction from G-strand regulation not fully defined"]},{"year":2012,"claim":"Showed Cdc13 OB2 dimerization is required for productive CST assembly and capping, adding an assembly determinant upstream of Stn1.","evidence":"Crystallography, biochemical binding and in vivo telomere length assays in yeast","pmids":["23177925"],"confidence":"High","gaps":["Human CTC1 equivalent of OB2 dimerization not addressed","Single-lab structural study"]},{"year":2013,"claim":"Solved the human STN1–TEN1 structure, confirming RPA-like architecture, assigning ssDNA binding mainly to STN1, and establishing TEN1 as required for CST telomeric function.","evidence":"X-ray crystallography, in vitro ssDNA binding and cell-based telomere assays with dimerization-defective mutants","pmids":["23826127"],"confidence":"High","gaps":["Full CTC1-containing trimer structure unsolved","Conformational changes on DNA binding not captured"]},{"year":2013,"claim":"Identified Cdk1 phosphorylation of Stn1 as a cell-cycle timing switch controlling CST-versus-telomerase recruitment at telomeres.","evidence":"In vitro kinase assay, phospho-site mutagenesis, ChIP and telomere length assay in yeast","pmids":["24164896"],"confidence":"High","gaps":["Whether human STN1 is analogously regulated by Cdk1 untested here","Downstream effector of phospho-Stn1 unclear"]},{"year":2014,"claim":"Defined the mechanism of CST stimulation of Pol α-primase, showing purified CST/Stn1 augments primase activity and primase-to-polymerase switching via direct Pol12/POLA2 binding through both OB and WH domains.","evidence":"Fully reconstituted in vitro primase and switch assays with purified Candida CST and domain dissection","pmids":["25503194"],"confidence":"High","gaps":["Structural basis of the Stn1–Pol12 contact not solved here","Coupling of stimulation to telomerase repression mechanistically separate"]},{"year":2014,"claim":"Connected shelterin to CST recruitment, showing SUMOylation of the TPP1 ortholog Tpz1 increases its affinity for Stn1 and recruits Stn1–Ten1 to inhibit telomerase.","evidence":"SUMO-site mutagenesis, SUMO-fusion binding, telomere ChIP and length assays in fission yeast, independently replicated","pmids":["24711392","24925530"],"confidence":"High","gaps":["Whether a SUMO-TPP1–STN1 axis operates in human cells untested","SUMO E3 ligase responsible not pinpointed here"]},{"year":2014,"claim":"Established Stn1–Ten1 as the essential core capping unit able to act independently of Cdc13 under altered stoichiometry.","evidence":"Genetic epistasis with NMD pathway, Stn1 ChIP and telomere ssDNA assays in yeast","pmids":["24835988"],"confidence":"Medium","gaps":["Physiological relevance of Cdc13-independent binding unclear","Single-lab epistasis evidence"]},{"year":2016,"claim":"Separated CST functions using an OB-fold mutant, showing short-ssDNA binding is needed for resolving endogenous replication stress and telomere duplex replication but not C-strand fill-in.","evidence":"In vitro ssDNA binding plus STN1 mutant cell-based replication assays","pmids":["27690379"],"confidence":"High","gaps":["Molecular determinants distinguishing the two activities undefined","Substrate-length selectivity mechanism unresolved"]},{"year":2017,"claim":"Pinned human STN1's Pol α stimulation to its N-terminal OB fold binding POLA2's central OB fold, and showed a disease mutation selectively abolishes this, establishing clinical relevance.","evidence":"Reconstituted PP stimulation, pull-down domain mapping and disease-mutant analysis with purified human proteins","pmids":["28934486"],"confidence":"High","gaps":["Structure of the STN1–POLA2 interface not solved","How POLA2 OB displacement gates the active site not visualized"]},{"year":2018,"claim":"Dissected individual CST subunit roles, showing CTC1–STN1 limits telomerase G-overhang extension while TEN1 is separately essential for C-strand synthesis and stabilizes DNA binding.","evidence":"CRISPR knockout of single subunits, overhang and telomerase ChIP and in vitro DNA binding in human cells","pmids":["30026550","29774655"],"confidence":"High","gaps":["How TEN1 contributes to C-strand synthesis biochemically unresolved","Order of telomerase termination and fill-in unclear"]},{"year":2018,"claim":"Identified a SUMO-interacting motif in Stn1's C-terminus required for SUMO-Tpz1 binding and telomerase inhibition, completing the SUMO-dependent recruitment mechanism.","evidence":"SIM mutagenesis, SUMO interaction, telomere and telomerase ChIP and length assays in fission yeast","pmids":["29774234"],"confidence":"High","gaps":["SIM conservation in mammalian STN1 not addressed","Relationship of SIM to DNA-binding function unclear"]},{"year":2021,"claim":"Identified the STN1 intrinsically disordered region as essential for replication-stress genome stability and Pol α interaction, separable from CST assembly and RAD51 binding.","evidence":"IDR mutagenesis, viability, RAD51 foci, co-IP and HU sensitivity in cells","pmids":["34681076"],"confidence":"Medium","gaps":["How the IDR promotes RAD51 loading mechanistically unknown","Single-lab evidence"]},{"year":2022,"claim":"Linked yeast Stn1 to origin firing through the MCM helicase, proposing it acts as an accessory replication factor facilitating MCM activation.","evidence":"Genetic epistasis with mcm alleles, suppressor analysis and origin firing/ssDNA assays in yeast","pmids":["35150303"],"confidence":"Medium","gaps":["No direct Stn1–MCM physical interaction shown","Conservation in human cells untested"]},{"year":2023,"claim":"Defined a phospho-regulated fork-protection role, showing ATR–CHK1 and CaMKK2 phosphorylate STN1's IDR to recruit it to stalled forks and block MRE11-mediated degradation.","evidence":"In vitro kinase assays, phospho-mutants, iPOND/fiber fork protection and MRE11/RAD51 fork ChIP","pmids":["38036565"],"confidence":"High","gaps":["How phospho-STN1 physically excludes MRE11 unresolved","Interplay with CST DNA binding at forks unclear"]},{"year":2023,"claim":"Uncovered a non-telomeric STN1–BER axis, showing STN1 loss downregulates DNA glycosylases and causes oxidative DNA damage in colon tissue.","evidence":"Conditional STN1 knockout mouse, BER activity, glycosylase expression and oxidative damage assays","pmids":["37163605"],"confidence":"Medium","gaps":["Mechanism by which STN1 controls glycosylase expression unknown","Direct vs indirect regulation unresolved"]},{"year":2025,"claim":"Established CST as a regulator of DSB end resection, suppressing EXO1 and BLM–DNA2 via distinct mechanisms and modulating BRCA1 status and PARP-inhibitor sensitivity.","evidence":"Biochemical resection reconstitution, CST mutant separation and cell-based PARPi resistance assays","pmids":["40403056"],"confidence":"High","gaps":["Structural basis of CST–BLM/EXO1 contacts undefined","How BRCA1-BARD1 relieves only the EXO1 block unresolved"]},{"year":2025,"claim":"Revealed a CST-independent transcriptional role, with STN1 displacing R-loop-flanking ssDNA to recruit STAT3 and activate ZEB1, driving EMT and metastasis.","evidence":"Co-IP, ChIP, R-loop detection, ZEB1 reporter and STAT3 inhibitor rescue in pancreatic cancer models","pmids":["40841373"],"confidence":"Medium","gaps":["Generality beyond PDAC unknown","Direct demonstration of ssDNA displacement at promoters limited"]},{"year":2025,"claim":"Showed STN1 stabilizes CTC1 by competing with TRIM32 for the same OB-G binding region, preventing CTC1 ubiquitination and degradation.","evidence":"Co-IP, ubiquitination assay, proteasome inhibitor rescue and AlphaFold3 modeling","pmids":["40923710"],"confidence":"Medium","gaps":["Binding interface inferred from modeling not experimental structure","Physiological conditions triggering competition unclear"]},{"year":2025,"claim":"Demonstrated a CST-independent STN1–ATM axis required for both HR and NHEJ DSB repair and the G2/M checkpoint after irradiation.","evidence":"Proteomic interaction screen, ATM expression/signaling, HR/NHEJ reporter and checkpoint assays","pmids":["41036624"],"confidence":"Medium","gaps":["How STN1 stabilizes ATM mechanistically unknown","Single-lab interaction data"]},{"year":2025,"claim":"Confirmed in human cells that STN1 limits telomerase-mediated G-overhang extension, with knockout phenotypes rescued by telomerase inhibition.","evidence":"Conditional CRISPR knockout, overhang and telomere damage assays with telomerase inhibition rescue","pmids":["42148867"],"confidence":"High","gaps":["Molecular step at which STN1 terminates telomerase unresolved","Contribution of C-strand fill-in defects to instability not separated"]},{"year":2026,"claim":"Extended STN1's transcriptional function to germ cell development, showing it partners with Tcf/Lef to enhance Wnt/β-catenin signaling required for oocyte survival.","evidence":"Co-IP, ChIP at germ cell promoters, conditional knockout and Wnt reporter in zebrafish","pmids":["41998405"],"confidence":"Medium","gaps":["Whether this role exists in mammals unknown","Mechanistic link between ssDNA binding and Tcf/Lef recruitment unclear"]},{"year":null,"claim":"How STN1's many CST-independent activities (transcriptional activation, ATM stabilization, BER regulation) are coordinated with its telomeric and fork-protection roles, and whether a unified DNA/RNA-binding mechanism underlies them, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the full CTC1–STN1–TEN1 trimer on DNA","Mechanistic unification of telomeric and non-telomeric functions lacking","Determinants directing STN1 between ssDNA, R-loops and protein partners undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[5,6,14,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[16,21,22,29]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[7,14]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[30,34]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[3,4,6,9]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,30]}],"pathway":[{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[11,12,16,21]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[27,28,29,32]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[15,32]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[30,34]}],"complexes":["CST (CTC1-STN1-TEN1)"],"partners":["CTC1","TEN1","POLA2","CDC13","STAT3","ATM","TRIM32","TPP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H668","full_name":"CST complex subunit STN1","aliases":["Oligonucleotide/oligosaccharide-binding fold-containing protein 1","Suppressor of cdc thirteen homolog"],"length_aa":368,"mass_kda":42.1,"function":"Component of the CST complex proposed to act as a specialized replication factor promoting DNA replication under conditions of replication stress or natural replication barriers such as the telomere duplex. The CST complex binds single-stranded DNA with high affinity in a sequence-independent manner, while isolated subunits bind DNA with low affinity by themselves. Initially the CST complex has been proposed to protect telomeres from DNA degradation (PubMed:19854130). However, the CST complex has been shown to be involved in several aspects of telomere replication. The CST complex inhibits telomerase and is involved in telomere length homeostasis; it is proposed to bind to newly telomerase-synthesized 3' overhangs and to terminate telomerase action implicating the association with the ACD:POT1 complex thus interfering with its telomerase stimulation activity. The CST complex is also proposed to be involved in fill-in synthesis of the telomeric C-strand probably implicating recruitment and activation of DNA polymerase alpha (PubMed:22763445, PubMed:22964711). The CST complex facilitates recovery from many forms of exogenous DNA damage; seems to be involved in the re-initiation of DNA replication at repaired forks and/or dormant origins (PubMed:25483097). Required for efficicient replication of the duplex region of the telomere. Promotes efficient replication of lagging-strand telomeres (PubMed:22863775, PubMed:22964711). Promotes general replication start following replication-fork stalling implicating new origin firing (PubMed:22863775). May be in involved in C-strand fill-in during late S/G2 phase independent of its role in telomere duplex replication (PubMed:23142664) Component of the CST complex, a complex that binds to single-stranded DNA and is required to protect telomeres from DNA degradation. The CST complex binds single-stranded DNA with high affinity in a sequence-independent manner, while isolated subunits bind DNA with low affinity by themselves. In addition to telomere protection, the CST complex has probably a more general role in DNA metabolism at non-telomeric sites","subcellular_location":"Nucleus; Chromosome, telomere","url":"https://www.uniprot.org/uniprotkb/Q9H668/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STN1","classification":"Not Classified","n_dependent_lines":546,"n_total_lines":1208,"dependency_fraction":0.4519867549668874},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/STN1","total_profiled":1310},"omim":[{"mim_id":"620063","title":"DNA POLYMERASE ALPHA-2, ACCESSORY SUBUNIT; POLA2","url":"https://www.omim.org/entry/620063"},{"mim_id":"618030","title":"SHIELD COMPLEX, SUBUNIT 3; SHLD3","url":"https://www.omim.org/entry/618030"},{"mim_id":"618029","title":"SHIELD COMPLEX, SUBUNIT 2; SHLD2","url":"https://www.omim.org/entry/618029"},{"mim_id":"618028","title":"SHIELD COMPLEX, SUBUNIT 1; SHLD1","url":"https://www.omim.org/entry/618028"},{"mim_id":"617341","title":"CEREBRORETINAL MICROANGIOPATHY WITH CALCIFICATIONS AND CYSTS 2; CRMCC2","url":"https://www.omim.org/entry/617341"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/STN1"},"hgnc":{"alias_symbol":["FLJ22559","bA541N10.2"],"prev_symbol":["OBFC1"]},"alphafold":{"accession":"Q9H668","domains":[{"cath_id":"2.40.50.140","chopping":"15-92_119-178","consensus_level":"high","plddt":94.1902,"start":15,"end":178},{"cath_id":"1.10.10.980","chopping":"186-249_256-295","consensus_level":"high","plddt":85.4856,"start":186,"end":295},{"cath_id":"1.10.10.10","chopping":"298-368","consensus_level":"high","plddt":93.3173,"start":298,"end":368}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H668","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H668-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H668-F1-predicted_aligned_error_v6.png","plddt_mean":87.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STN1","jax_strain_url":"https://www.jax.org/strain/search?query=STN1"},"sequence":{"accession":"Q9H668","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H668.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H668/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H668"}},"corpus_meta":[{"pmid":"19854130","id":"PMC_19854130","title":"RPA-like 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analysis) and functions in telomere length regulation; loss of Stn1 function causes accumulation of single-stranded DNA in subtelomeric regions and activates the RAD9/MEC3 G2/M DNA damage checkpoints.\",\n      \"method\": \"Two-hybrid interaction, genetic suppressor screen, ssDNA detection assay, checkpoint genetic analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic and physical interaction data, replicated across multiple labs in subsequent work\",\n      \"pmids\": [\"9042864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Stn1 acts as an inhibitor of telomerase recruitment by Cdc13; a Cdc13-Stn1 fusion protein blocks telomere elongation, indicating Stn1 negatively regulates the telomerase-loading function of Cdc13.\",\n      \"method\": \"Fusion protein overexpression, telomere length assays, genetic epistasis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fusion protein and genetic experiments in single lab, two complementary approaches\",\n      \"pmids\": [\"11046137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Ten1 physically associates with both Stn1 and Cdc13; a binding defect between Stn1-13 and Ten1 underlies the long-telomere phenotype; Ten1 is required for telomere length regulation and preventing single-stranded DNA accumulation at telomeres.\",\n      \"method\": \"Two-hybrid interaction, genetic complementation, ssDNA assay, checkpoint analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal physical interaction, allele-specific genetic rescue, replicated by subsequent structural studies\",\n      \"pmids\": [\"11230140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Fission yeast Stn1 and Ten1 are essential for chromosome end protection and form a complex with each other but not with Pot1; they localize at telomeres in a manner correlated with ssDNA overhang length, and both contain OB-fold domains.\",\n      \"method\": \"Genetic deletion, co-immunoprecipitation, telomere localization assay, structural bioinformatics\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function genetics plus direct localization and protein interaction experiments, replicated across species\",\n      \"pmids\": [\"17715303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Stn1 has two separable functional domains: the N-terminus interacts with Ten1 and is essential for telomere capping, while the C-terminus binds both Cdc13 and Pol12 and is required to limit continuous telomerase action. Stn1 telomere association peaks in S phase.\",\n      \"method\": \"Domain dissection/truncation analysis, genetic complementation, chromatin immunoprecipitation, in vivo binding assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple domain mutants, orthogonal genetic and ChIP assays, two separable phenotypes established\",\n      \"pmids\": [\"19172739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Mammalian STN1 and TEN1 homologs were identified and shown to form the CST (CTC1-STN1-TEN1) complex that binds single-stranded DNA with high affinity in a sequence-independent manner; knockdown of Stn1 causes significant increases in single-stranded G-strand telomeric DNA.\",\n      \"method\": \"Protein identification, co-immunoprecipitation, ssDNA-binding assay, siRNA knockdown, telomere ssDNA quantification\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical complex reconstitution, binding assay, functional knockdown with defined telomeric phenotype\",\n      \"pmids\": [\"19854130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Human OBFC1 (STN1) associates with TPP1 in the telomere interactome, localizes to telomeres in human cells, binds telomeric single-stranded DNA in vitro, and overexpression of an OBFC1 mutant results in telomere elongation.\",\n      \"method\": \"Proteomic co-immunoprecipitation, telomere localization (FISH/immunofluorescence), in vitro DNA binding assay, overexpression telomere length assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulldown plus localization plus in vitro binding, single lab\",\n      \"pmids\": [\"19648609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the Candida tropicalis Stn1N-Ten1 complex shows an RPA2N-RPA3-like architecture with OB-fold packing; the C-terminal domain of S. cerevisiae Stn1 contains two WH motifs similar to RPA2-C. Mutations disrupting Stn1-Ten1 interaction cause telomere uncapping and abolish Ten1 telomere localization.\",\n      \"method\": \"X-ray crystallography, mutational analysis, telomere localization assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures from multiple species plus functional mutagenesis validation\",\n      \"pmids\": [\"20008938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"AtCTC1 (plant CTC1) physically and genetically interacts with AtSTN1; both are required for telomere integrity in Arabidopsis. Human CTC1 depletion by RNAi triggers DNA damage response and telomere defects, demonstrating conservation of the CST complex.\",\n      \"method\": \"Co-immunoprecipitation, genetic interaction, RNAi knockdown, telomere analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — physical and genetic interaction corroborated across plant and human systems, independent of PMID:19854130\",\n      \"pmids\": [\"19854131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Overproduction of yeast Stn1 blocks S-phase checkpoint functions downstream of Rad53 activation; Stn1 broadly associates with chromosomes and its checkpoint-overriding effect depends on Pol12 (a subunit of DNA Pol α), indicating Stn1 promotes Pol α activity genome-wide when overproduced.\",\n      \"method\": \"Overexpression analysis, checkpoint kinase activation assay, chromatin binding assay, pol12 genetic rescue\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with pol12 plus chromatin binding, single lab\",\n      \"pmids\": [\"19171895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Structural prediction and mutagenesis of a predicted alpha-helix in the N-terminal OB fold of S. cerevisiae Stn1 identified a specific Stn1-Ten1 interaction interface; stn1-L164D eliminates Ten1 association and is specifically suppressed by ten1-D138Y, confirming the interface.\",\n      \"method\": \"Structure-based mutagenesis, two-hybrid interaction, allele-specific suppression genetics\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — allele-specific suppression (strong genetic evidence) plus binding assay, single lab\",\n      \"pmids\": [\"20157006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Xenopus CST (xCST) is involved in priming DNA synthesis on ssDNA templates in egg extracts; immunodepletion of xStn1 does not impair replication of chromatin DNA but specifically blocks the priming step on ssDNA templates, consistent with a role in telomeric C-strand synthesis regulation of Pol α-primase.\",\n      \"method\": \"Xenopus egg extract reconstitution, immunodepletion, in vitro DNA synthesis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with immunodepletion, primed vs. unprimed substrate comparison, single lab\",\n      \"pmids\": [\"22086929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human Stn1 depletion causes catastrophic telomere shortening and DNA damage specifically at lagging-strand telomeres; hStn1 promotes efficient replication of lagging-strand telomeric DNA, and its loss leads to persistent/elevated association of DNA Pol α with telomeres, suggesting hStn1 modulates Pol α synthesis activity rather than controlling its loading.\",\n      \"method\": \"shRNA knockdown, BrdU incorporation/FISH, telomere fragility assay, ChIP for Pol α\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with multiple orthogonal readouts, strand-specific phenotype established, reproduced in subsequent studies\",\n      \"pmids\": [\"22964711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Cdc13 OB2 domain forms a homodimer; disruption of OB2 dimerization (e.g., by cdc13-1 mutation) impairs Cdc13-Stn1 association and causes telomere length deregulation, establishing that Cdc13 OB2 dimerization is required for proper CST assembly and productive telomere capping.\",\n      \"method\": \"X-ray crystallography, biochemical binding assay, in vivo telomere length assay, mutagenesis\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biochemical validation and in vivo functional assay, single lab\",\n      \"pmids\": [\"23177925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of the human STN1-TEN1 complex reveals hSTN1 with an OB domain and tandem C-terminal wHTH motifs, and hTEN1 with a single OB fold; the complex is structurally similar to RPA. hSTN1 is primarily responsible for ssDNA binding; cells expressing hSTN1 dimerization-defective mutants show elongated telomeres and telomere uncapping defects, indicating hTEN1 is required for hCST telomeric function.\",\n      \"method\": \"X-ray crystallography, in vitro ssDNA binding assay, cell-based telomere length and damage assay, mutagenesis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis plus functional cell-based assays\",\n      \"pmids\": [\"23826127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Cdk1 phosphorylates Stn1 at threonine 223 and serine 250 in vitro and in vivo; these phosphorylations are essential for stability of CST complexes at telomeres and regulate the temporal recruitment of CST versus telomerase complexes during the cell cycle.\",\n      \"method\": \"In vitro kinase assay, phospho-site mutagenesis, chromatin immunoprecipitation, telomere length assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation confirmed in vivo, phospho-mutants tested for CST telomere association, single lab\",\n      \"pmids\": [\"24164896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Purified CST from Candida glabrata substantially augments primase activity and primase-to-polymerase switching of the primase-Pol α (PP) complex; CST shortens RNA and lengthens DNA in chimeric products. Stn1 alone is sufficient for PP stimulation, acting through both its N-terminal OB fold and C-terminal WH domains via direct binding to the Pol12 subunit of PP.\",\n      \"method\": \"In vitro biochemical reconstitution with purified complexes, primase assay, primase-to-polymerase switch assay, binding assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — fully reconstituted in vitro system with purified components, domain dissection, mechanism defined\",\n      \"pmids\": [\"25503194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SUMOylation of fission yeast shelterin subunit Tpz1 (TPP1 ortholog) on lysine 242 promotes recruitment of Stn1-Ten1 to telomeres and prevents telomerase accumulation, establishing a SUMO-dependent pathway that links shelterin to CST-mediated telomerase inhibition.\",\n      \"method\": \"SUMOylation site mutagenesis, telomere ChIP for Stn1 and telomerase, telomere length assay, SUMO-fusion protein binding assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — site-specific mutagenesis plus ChIP plus SUMO-fusion binding assay, independently confirmed in separate study (PMID:24925530)\",\n      \"pmids\": [\"24711392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Fission yeast Tpz1 (TPP1 ortholog) SUMOylation promotes Stn1 telomere association via direct increased affinity of SUMO-Tpz1 for Stn1, independently confirmed and showing evolutionary conservation of SUMO-dependent CST recruitment.\",\n      \"method\": \"Protein interaction assay (SUMO-fusion pulldown), telomere ChIP, telomere length assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding assay plus ChIP, replicates PMID:24711392 finding with orthogonal approach\",\n      \"pmids\": [\"24925530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Stn1 and Ten1 can function in a Cdc13-independent manner; disabling NMD alters CST stoichiometry at telomeres and permits Stn1 to bind telomeres without Cdc13, establishing Stn1 and Ten1 as the essential core of the CST capping complex.\",\n      \"method\": \"Genetic epistasis (NMD/DDR pathway mutations), ChIP for Stn1, telomere ssDNA assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis plus ChIP, single lab, mechanistic conclusion supported by two approaches\",\n      \"pmids\": [\"24835988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"An OB-fold mutation in STN1 (STN1-OBM) preferentially destabilizes binding to short ssDNA substrates and selectively impairs resolution of endogenous replication stress and telomere duplex replication in vivo, but does not affect telomeric C-strand fill-in or origin firing after exogenous replication stress, indicating mechanistic differences in CST action at different replication problems.\",\n      \"method\": \"In vitro ssDNA binding assay, STN1 mutant cell-based phenotypic analysis, telomere replication assay\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro binding combined with multiple in vivo functional assays, separation-of-function mutant\",\n      \"pmids\": [\"27690379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Human STN1 alone (purified) stimulates primase-Pol α (PP) activity in vitro primarily through its N-terminal OB fold by binding POLA2; the STN1-POLA2 interaction targets the central OB fold domain of POLA2, which in the substrate-free PP structure blocks nucleic acid entry to the Pol α active site. A disease-causing STN1 mutation selectively disrupts POLA2 binding and PP stimulation.\",\n      \"method\": \"In vitro PP stimulation assay with purified proteins, pull-down binding assay, disease mutant analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro biochemical assay, domain mapping, disease mutation validates functional relevance\",\n      \"pmids\": [\"28934486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CTC1-STN1 together limits telomerase action to prevent G-overhang overextension; TEN1 is separately essential for C-strand synthesis. CTC1-STN1 retains ssDNA affinity without TEN1 but TEN1 stabilizes binding; CTC1-STN1 binding to DNA Pol α is required to fully repress telomerase activity.\",\n      \"method\": \"CRISPR/Cas9 knockout of individual CST subunits, telomere overhang analysis, telomerase recruitment ChIP, in vitro DNA binding assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic dissection of individual subunit contributions, multiple orthogonal readouts, corroborated in PMID:29774655\",\n      \"pmids\": [\"30026550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CRISPR-engineered CTC1-L1142H (Coats plus mutation) disrupts CTC1-STN1 interaction, leading to telomerase-mediated telomere elongation; impaired CTC1:STN1-DNA Pol α binding further de-represses telomerase; CP CTC1 mutants failing to interact with Pol α cause loss of C-strand maintenance and catastrophic telomere shortening.\",\n      \"method\": \"CRISPR/Cas9 knock-in, co-immunoprecipitation, telomere length assay, telomerase recruitment ChIP, Pol α interaction assay\",\n      \"journal\": \"Aging cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous knock-in mutation with multiple functional assays, consistent with PMID:30026550\",\n      \"pmids\": [\"29774655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Fission yeast Stn1 contains a SUMO-interacting motif (SIM) in its C-terminal domain that is required for interaction with SUMO and SUMO-Tpz1; SIM point mutations (Stn1-226) cause telomere elongation, impair Stn1-Ten1 recruitment to telomeres, and enhance telomerase binding, establishing the SIM as critical for telomerase inhibition at chromosome ends.\",\n      \"method\": \"SIM mutagenesis, SUMO interaction assay, telomere ChIP, telomere length assay, telomerase ChIP\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — point mutations in defined motif, multiple orthogonal assays (binding, ChIP, length), consistent with independent SUMO pathway studies\",\n      \"pmids\": [\"29774234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The intrinsically disordered region (IDR) within the STN1 OB-fold domain is critical for maintaining genome stability under replication stress; single IDR mutations cause genome instability and reduced viability, reduce RAD51 foci under replication stress, and impair STN1-POL α interaction, without affecting CST complex formation or STN1-RAD51 direct binding.\",\n      \"method\": \"Site-directed mutagenesis, cell viability assay, RAD51 foci immunofluorescence, co-immunoprecipitation, HU sensitivity assay\",\n      \"journal\": \"Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with multiple cellular phenotype readouts, single lab\",\n      \"pmids\": [\"34681076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Yeast Stn1 overproduction circumvents Rad53 S-phase checkpoint through the MCM complex; Mcm2/Mcm5 mutations block Stn1-overproduction checkpoint bypass, loss-of-function stn1 mutations compensate rad53 defects, and Stn1 overproduction suppresses mcm7 mutants, indicating Stn1 functions as an accessory replication factor facilitating MCM activation at origins.\",\n      \"method\": \"Genetic epistasis, suppressor analysis, origin firing assay, ssDNA accumulation assay\",\n      \"journal\": \"Current genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple MCM alleles, single lab\",\n      \"pmids\": [\"35150303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STN1 is phosphorylated by both ATR-CHK1 and CaMKK2 in its intrinsically disordered region in response to replication stress (hydroxyurea/aphidicolin or elevated cytosolic calcium); loss of STN1 phosphorylation reduces STN1 localization to stalled forks, elevates nascent strand degradation, increases MRE11 access, and decreases RAD51 at forks.\",\n      \"method\": \"In vitro kinase assay, phospho-site mutagenesis, fork protection assay (iPOND/fiber), MRE11/RAD51 ChIP at forks\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay validated in vivo, phospho-mutant functional analysis with multiple orthogonal readouts\",\n      \"pmids\": [\"38036565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STN1 deficiency down-regulates multiple DNA glycosylases, resulting in defective base excision repair (BER) and accumulation of oxidative DNA damage, identifying a STN1-BER axis that protects colon tissue.\",\n      \"method\": \"Conditional STN1 knockout mouse model, BER activity assay, DNA glycosylase expression analysis, oxidative damage quantification\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional KO with defined BER mechanistic readout, single lab\",\n      \"pmids\": [\"37163605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The CST complex suppresses DNA end resection by EXO1 and the BLM-DNA2 helicase-nuclease complex via distinct mechanisms; BRCA1-BARD1 alleviates the CST-imposed EXO1 blockade but has little effect on BLM-DNA2 restriction. CST mutants impaired for DNA binding or BLM-EXO1 interaction exhibit hyper-resection and render BRCA1-deficient cells resistant to PARP inhibitors.\",\n      \"method\": \"Biochemical resection assay, CST DNA-binding and protein-interaction mutant analysis, cell-based PARPi resistance assay\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution of resection suppression, mechanistic mutant separation, functional cell-based validation\",\n      \"pmids\": [\"40403056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STN1 directly interacts with the transcription factor STAT3 and structurally displaced ssDNA flanking R-loops at gene promoters, recruiting STAT3 to activate ZEB1 transcription independently of its telomere maintenance function, thereby promoting EMT and metastasis in pancreatic cancer.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, R-loop detection, ZEB1 reporter assay, STAT3 inhibitor rescue\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and ChIP in multiple PDAC models, single lab, non-telomeric function\",\n      \"pmids\": [\"40841373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STN1 directly interacts with CTC1 at the OB-G domain and competes with TRIM32 for the same binding region; STN1 binding prevents TRIM32-mediated ubiquitination and proteasomal degradation of CTC1, thereby stabilizing the CST complex.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor rescue, structural modeling (AlphaFold3)\",\n      \"journal\": \"Aging cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and ubiquitination assay, single lab, structural model supporting but not definitively confirming binding interface\",\n      \"pmids\": [\"40923710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STN1 interacts with ATM and stabilizes ATM expression and signaling after DNA damage; STN1 silencing reduces both homologous recombination and non-homologous end joining repair of DSBs and impairs G2/M checkpoint arrest after ionizing radiation, in a CST complex-independent manner.\",\n      \"method\": \"Co-immunoprecipitation/proteomic interaction screen, ATM expression/signaling assay, HR/NHEJ reporter assay, cell cycle checkpoint assay after IR\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic interaction plus functional DSB repair assays, single lab\",\n      \"pmids\": [\"41036624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conditional deletion of human STN1 causes proliferation defects, telomeric damage signaling, G-overhang overextension, and genome instability (anaphase bridges, micronuclei); these phenotypes are largely dependent on telomerase activity, establishing that STN1 limits telomerase-mediated G-overhang extension.\",\n      \"method\": \"Conditional CRISPR/Cas9 knockout, telomere overhang assay, telomere damage focus quantification, telomerase inhibition rescue\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple phenotypic readouts and genetic rescue by telomerase inhibition\",\n      \"pmids\": [\"42148867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In zebrafish, Stn1 interacts with the transcription factor Tcf/Lef, facilitates its association with promoters of germ cell-specific genes, and enhances Wnt/β-catenin signaling activity in oocytes; genetic deletion of stn1 leads to massive oocyte loss.\",\n      \"method\": \"Co-immunoprecipitation, ChIP at germ cell promoters, conditional genetic knockout, Wnt pathway reporter assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and ChIP plus genetic KO with phenotypic rescue, single organism/lab\",\n      \"pmids\": [\"41998405\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STN1 (OBFC1) is a core subunit of the RPA-like CST (CTC1-STN1-TEN1) heterotrimeric complex that binds single-stranded DNA via OB-fold domains; its N-terminal OB fold and intrinsically disordered region support ssDNA binding, Pol α-primase stimulation (by direct interaction with POLA2/Pol12), and fork protection, while its C-terminal winged-helix domain interacts with Cdc13/CTC1 and Ten1 to assemble the CST complex; at telomeres, CTC1-STN1 terminates telomerase-mediated G-overhang extension and—together with TEN1—promotes C-strand fill-in by DNA Pol α-primase; STN1 phosphorylation by ATR-CHK1 and CaMKK2 enables its recruitment to stalled replication forks where it blocks MRE11-mediated nascent strand degradation; CST additionally suppresses DSB end resection by EXO1 and BLM-DNA2 to direct break repair pathway choice; STN1 also stabilizes CTC1 by competing with the E3 ubiquitin ligase TRIM32, and harbors non-telomeric functions including regulation of base excision repair, ATM-dependent DSB repair, and transcriptional activation via R-loop-associated ssDNA binding.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"STN1 is a core subunit of the conserved RPA-like CST (CTC1–STN1–TEN1) complex that binds single-stranded DNA via OB-fold domains and governs telomere end protection and genome-wide replication [#5, #14]. It was first defined in budding yeast through physical and genetic interaction with Cdc13, where loss of Stn1 causes subtelomeric ssDNA accumulation and checkpoint activation [#0], and through its negative regulation of Cdc13-mediated telomerase recruitment [#1]. STN1 partitions into separable modules: its N-terminal OB fold heterodimerizes with TEN1 in an RPA2N–RPA3-like architecture essential for telomere capping, while its C-terminal tandem winged-helix domains engage Cdc13/CTC1 and the Pol12/POLA2 subunit of DNA polymerase α-primase to limit telomerase action [#4, #7, #14]. At chromosome ends CTC1–STN1 terminates telomerase-mediated G-overhang extension while TEN1-assisted CST promotes C-strand fill-in by stimulating the priming and primase-to-polymerase switch of Pol α-primase through direct binding to POLA2, a stimulation STN1 can drive on its own [#16, #21, #22, #33]. Beyond telomeres, STN1 is recruited to stalled replication forks following ATR–CHK1 and CaMKK2 phosphorylation of its intrinsically disordered region, where it blocks MRE11-mediated nascent-strand degradation and maintains RAD51 [#25, #27], and CST suppresses DSB end resection by EXO1 and BLM–DNA2 to influence repair-pathway choice and PARP-inhibitor sensitivity [#29]. STN1 additionally stabilizes CTC1 by competing with the E3 ligase TRIM32 [#31] and carries CST-independent roles spanning base excision repair, ATM-dependent DSB repair, and R-loop-associated transcriptional activation via STAT3 and Tcf/Lef [#28, #30, #32, #34]. A disease-causing STN1 mutation that selectively disrupts POLA2 binding links the Pol α-stimulating function to Coats plus–spectrum telomere pathology [#21, #23].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established Stn1 as a telomere-associated factor by showing it binds Cdc13 and that its loss produces subtelomeric ssDNA and checkpoint activation, defining a capping rather than length-only function.\",\n      \"evidence\": \"Two-hybrid interaction, genetic suppressor screen, ssDNA detection and checkpoint analysis in budding yeast\",\n      \"pmids\": [\"9042864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of Cdc13–Stn1 binding undefined\", \"No biochemical demonstration of ssDNA binding by Stn1 itself\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Resolved whether Stn1 promotes or restrains telomerase, showing it is a negative regulator of Cdc13-dependent telomerase loading.\",\n      \"evidence\": \"Cdc13-Stn1 fusion overexpression and telomere length/epistasis assays in yeast\",\n      \"pmids\": [\"11046137\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Fusion protein may not reflect endogenous regulation\", \"Mechanism of telomerase exclusion not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified Ten1 as the third partner, establishing a three-component capping module and that Stn1–Ten1 contacts are required to restrain telomere length.\",\n      \"evidence\": \"Two-hybrid, allele-specific genetic rescue, ssDNA and checkpoint assays in yeast\",\n      \"pmids\": [\"11230140\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structure of the trimer unknown\", \"Direct DNA-binding role of each subunit unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed conservation in fission yeast and that Stn1–Ten1 form an OB-fold complex independent of Pot1, positioning CST as a distinct end-protection entity.\",\n      \"evidence\": \"Gene deletion, co-IP, telomere localization and structural bioinformatics in fission yeast\",\n      \"pmids\": [\"17715303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"OB-fold predictions not yet structurally confirmed\", \"Relationship to Pol α not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mapped Stn1 into separable N-terminal (Ten1/capping) and C-terminal (Cdc13/Pol12/telomerase-limiting) functional domains, dissecting its dual roles.\",\n      \"evidence\": \"Truncation/domain mutagenesis, genetic complementation and ChIP in yeast\",\n      \"pmids\": [\"19172739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural interfaces unresolved\", \"How Pol12 binding limits telomerase mechanistically unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended CST to mammals and plants, defining the human CTC1–STN1–TEN1 complex as a high-affinity sequence-independent ssDNA binder whose loss elevates telomeric G-strand ssDNA.\",\n      \"evidence\": \"Complex purification, co-IP, ssDNA-binding, siRNA/RNAi knockdown, telomere interactome proteomics across human, plant and yeast\",\n      \"pmids\": [\"19854130\", \"19648609\", \"19854131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which subunit carries primary DNA-binding activity not yet assigned\", \"Telomerase-regulation mechanism in human cells undefined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked Stn1 to genome-wide Pol α activity by showing its overproduction overrides the S-phase checkpoint in a Pol12-dependent manner.\",\n      \"evidence\": \"Overexpression, Rad53 activation assay, chromatin binding and pol12 genetic rescue in yeast\",\n      \"pmids\": [\"19171895\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression phenotype may not mirror physiological role\", \"Direct effect on Pol α biochemistry not shown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Provided the first structural framework, showing Stn1N–Ten1 adopts an RPA2N–RPA3-like fold and that disrupting this interface causes uncapping.\",\n      \"evidence\": \"X-ray crystallography of Candida Stn1N–Ten1 plus mutational telomere localization assays\",\n      \"pmids\": [\"20008938\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length trimer structure unsolved\", \"C-terminal WH domain functions not structurally defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Refined the Stn1–Ten1 interface to a specific N-terminal helix via allele-specific suppression, validating the structural model genetically.\",\n      \"evidence\": \"Structure-based mutagenesis, two-hybrid and allele-specific suppression in yeast\",\n      \"pmids\": [\"20157006\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab genetic data\", \"Interface conservation in human STN1 not tested here\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated that vertebrate CST specifically supports priming of DNA synthesis on ssDNA templates, connecting Stn1 directly to Pol α-primase function.\",\n      \"evidence\": \"Xenopus egg extract reconstitution with xStn1 immunodepletion and in vitro DNA synthesis assays\",\n      \"pmids\": [\"22086929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct Pol α-binding partner not yet identified\", \"Telomere specificity vs general priming unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established that human STN1 is required for efficient lagging-strand telomere replication and modulates Pol α synthesis rather than its loading.\",\n      \"evidence\": \"shRNA knockdown, BrdU/FISH, telomere fragility and Pol α ChIP in human cells\",\n      \"pmids\": [\"22964711\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which STN1 modulates Pol α activity unresolved\", \"Distinction from G-strand regulation not fully defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed Cdc13 OB2 dimerization is required for productive CST assembly and capping, adding an assembly determinant upstream of Stn1.\",\n      \"evidence\": \"Crystallography, biochemical binding and in vivo telomere length assays in yeast\",\n      \"pmids\": [\"23177925\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human CTC1 equivalent of OB2 dimerization not addressed\", \"Single-lab structural study\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Solved the human STN1–TEN1 structure, confirming RPA-like architecture, assigning ssDNA binding mainly to STN1, and establishing TEN1 as required for CST telomeric function.\",\n      \"evidence\": \"X-ray crystallography, in vitro ssDNA binding and cell-based telomere assays with dimerization-defective mutants\",\n      \"pmids\": [\"23826127\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full CTC1-containing trimer structure unsolved\", \"Conformational changes on DNA binding not captured\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified Cdk1 phosphorylation of Stn1 as a cell-cycle timing switch controlling CST-versus-telomerase recruitment at telomeres.\",\n      \"evidence\": \"In vitro kinase assay, phospho-site mutagenesis, ChIP and telomere length assay in yeast\",\n      \"pmids\": [\"24164896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether human STN1 is analogously regulated by Cdk1 untested here\", \"Downstream effector of phospho-Stn1 unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the mechanism of CST stimulation of Pol α-primase, showing purified CST/Stn1 augments primase activity and primase-to-polymerase switching via direct Pol12/POLA2 binding through both OB and WH domains.\",\n      \"evidence\": \"Fully reconstituted in vitro primase and switch assays with purified Candida CST and domain dissection\",\n      \"pmids\": [\"25503194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the Stn1–Pol12 contact not solved here\", \"Coupling of stimulation to telomerase repression mechanistically separate\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected shelterin to CST recruitment, showing SUMOylation of the TPP1 ortholog Tpz1 increases its affinity for Stn1 and recruits Stn1–Ten1 to inhibit telomerase.\",\n      \"evidence\": \"SUMO-site mutagenesis, SUMO-fusion binding, telomere ChIP and length assays in fission yeast, independently replicated\",\n      \"pmids\": [\"24711392\", \"24925530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether a SUMO-TPP1–STN1 axis operates in human cells untested\", \"SUMO E3 ligase responsible not pinpointed here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established Stn1–Ten1 as the essential core capping unit able to act independently of Cdc13 under altered stoichiometry.\",\n      \"evidence\": \"Genetic epistasis with NMD pathway, Stn1 ChIP and telomere ssDNA assays in yeast\",\n      \"pmids\": [\"24835988\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of Cdc13-independent binding unclear\", \"Single-lab epistasis evidence\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Separated CST functions using an OB-fold mutant, showing short-ssDNA binding is needed for resolving endogenous replication stress and telomere duplex replication but not C-strand fill-in.\",\n      \"evidence\": \"In vitro ssDNA binding plus STN1 mutant cell-based replication assays\",\n      \"pmids\": [\"27690379\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinants distinguishing the two activities undefined\", \"Substrate-length selectivity mechanism unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Pinned human STN1's Pol α stimulation to its N-terminal OB fold binding POLA2's central OB fold, and showed a disease mutation selectively abolishes this, establishing clinical relevance.\",\n      \"evidence\": \"Reconstituted PP stimulation, pull-down domain mapping and disease-mutant analysis with purified human proteins\",\n      \"pmids\": [\"28934486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the STN1–POLA2 interface not solved\", \"How POLA2 OB displacement gates the active site not visualized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Dissected individual CST subunit roles, showing CTC1–STN1 limits telomerase G-overhang extension while TEN1 is separately essential for C-strand synthesis and stabilizes DNA binding.\",\n      \"evidence\": \"CRISPR knockout of single subunits, overhang and telomerase ChIP and in vitro DNA binding in human cells\",\n      \"pmids\": [\"30026550\", \"29774655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TEN1 contributes to C-strand synthesis biochemically unresolved\", \"Order of telomerase termination and fill-in unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a SUMO-interacting motif in Stn1's C-terminus required for SUMO-Tpz1 binding and telomerase inhibition, completing the SUMO-dependent recruitment mechanism.\",\n      \"evidence\": \"SIM mutagenesis, SUMO interaction, telomere and telomerase ChIP and length assays in fission yeast\",\n      \"pmids\": [\"29774234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SIM conservation in mammalian STN1 not addressed\", \"Relationship of SIM to DNA-binding function unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified the STN1 intrinsically disordered region as essential for replication-stress genome stability and Pol α interaction, separable from CST assembly and RAD51 binding.\",\n      \"evidence\": \"IDR mutagenesis, viability, RAD51 foci, co-IP and HU sensitivity in cells\",\n      \"pmids\": [\"34681076\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How the IDR promotes RAD51 loading mechanistically unknown\", \"Single-lab evidence\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked yeast Stn1 to origin firing through the MCM helicase, proposing it acts as an accessory replication factor facilitating MCM activation.\",\n      \"evidence\": \"Genetic epistasis with mcm alleles, suppressor analysis and origin firing/ssDNA assays in yeast\",\n      \"pmids\": [\"35150303\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct Stn1–MCM physical interaction shown\", \"Conservation in human cells untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a phospho-regulated fork-protection role, showing ATR–CHK1 and CaMKK2 phosphorylate STN1's IDR to recruit it to stalled forks and block MRE11-mediated degradation.\",\n      \"evidence\": \"In vitro kinase assays, phospho-mutants, iPOND/fiber fork protection and MRE11/RAD51 fork ChIP\",\n      \"pmids\": [\"38036565\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How phospho-STN1 physically excludes MRE11 unresolved\", \"Interplay with CST DNA binding at forks unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Uncovered a non-telomeric STN1–BER axis, showing STN1 loss downregulates DNA glycosylases and causes oxidative DNA damage in colon tissue.\",\n      \"evidence\": \"Conditional STN1 knockout mouse, BER activity, glycosylase expression and oxidative damage assays\",\n      \"pmids\": [\"37163605\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which STN1 controls glycosylase expression unknown\", \"Direct vs indirect regulation unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established CST as a regulator of DSB end resection, suppressing EXO1 and BLM–DNA2 via distinct mechanisms and modulating BRCA1 status and PARP-inhibitor sensitivity.\",\n      \"evidence\": \"Biochemical resection reconstitution, CST mutant separation and cell-based PARPi resistance assays\",\n      \"pmids\": [\"40403056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CST–BLM/EXO1 contacts undefined\", \"How BRCA1-BARD1 relieves only the EXO1 block unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed a CST-independent transcriptional role, with STN1 displacing R-loop-flanking ssDNA to recruit STAT3 and activate ZEB1, driving EMT and metastasis.\",\n      \"evidence\": \"Co-IP, ChIP, R-loop detection, ZEB1 reporter and STAT3 inhibitor rescue in pancreatic cancer models\",\n      \"pmids\": [\"40841373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality beyond PDAC unknown\", \"Direct demonstration of ssDNA displacement at promoters limited\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed STN1 stabilizes CTC1 by competing with TRIM32 for the same OB-G binding region, preventing CTC1 ubiquitination and degradation.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, proteasome inhibitor rescue and AlphaFold3 modeling\",\n      \"pmids\": [\"40923710\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface inferred from modeling not experimental structure\", \"Physiological conditions triggering competition unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated a CST-independent STN1–ATM axis required for both HR and NHEJ DSB repair and the G2/M checkpoint after irradiation.\",\n      \"evidence\": \"Proteomic interaction screen, ATM expression/signaling, HR/NHEJ reporter and checkpoint assays\",\n      \"pmids\": [\"41036624\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How STN1 stabilizes ATM mechanistically unknown\", \"Single-lab interaction data\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Confirmed in human cells that STN1 limits telomerase-mediated G-overhang extension, with knockout phenotypes rescued by telomerase inhibition.\",\n      \"evidence\": \"Conditional CRISPR knockout, overhang and telomere damage assays with telomerase inhibition rescue\",\n      \"pmids\": [\"42148867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular step at which STN1 terminates telomerase unresolved\", \"Contribution of C-strand fill-in defects to instability not separated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended STN1's transcriptional function to germ cell development, showing it partners with Tcf/Lef to enhance Wnt/β-catenin signaling required for oocyte survival.\",\n      \"evidence\": \"Co-IP, ChIP at germ cell promoters, conditional knockout and Wnt reporter in zebrafish\",\n      \"pmids\": [\"41998405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this role exists in mammals unknown\", \"Mechanistic link between ssDNA binding and Tcf/Lef recruitment unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How STN1's many CST-independent activities (transcriptional activation, ATM stabilization, BER regulation) are coordinated with its telomeric and fork-protection roles, and whether a unified DNA/RNA-binding mechanism underlies them, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the full CTC1–STN1–TEN1 trimer on DNA\", \"Mechanistic unification of telomeric and non-telomeric functions lacking\", \"Determinants directing STN1 between ssDNA, R-loops and protein partners undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [5, 6, 14, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [16, 21, 22, 29]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [7, 14]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [30, 34]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [3, 4, 6, 9]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 30]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [11, 12, 16, 21]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [27, 28, 29, 32]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [15, 32]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [30, 34]}\n    ],\n    \"complexes\": [\"CST (CTC1-STN1-TEN1)\"],\n    \"partners\": [\"CTC1\", \"TEN1\", \"POLA2\", \"Cdc13\", \"STAT3\", \"ATM\", \"TRIM32\", \"TPP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}