{"gene":"BUB1B","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2003,"finding":"CENP-E directly activates BubR1 kinase activity at kinetochores using purified components and Xenopus egg extracts; microtubule capture by the CENP-E motor domain silences BubR1 kinase activity in a ternary BubR1-CENP-E-microtubule complex, establishing CENP-E as the signal transducing linker that both activates and silences BubR1-dependent mitotic checkpoint signaling.","method":"In vitro reconstitution with purified BubR1, CENP-E, and microtubules; Xenopus egg extract immunodepletion and antibody-addition experiments","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with purified components, replicated across two independent experimental systems (extracts + purified proteins) in a single rigorous study","pmids":["12859900"],"is_preprint":false},{"year":2005,"finding":"Microtubule capture by CENP-E silences BubR1 kinase activity: a motorless fragment of CENP-E constitutively activates BubR1 at kinetochores producing checkpoint signaling not silenced by spindle capture or tension, whereas the motor domain of CENP-E silences BubR1 kinase in a ternary BubR1-CENP-E-microtubule complex in vitro.","method":"Biochemical reconstitution with purified BubR1, microtubules, and CENP-E; kinetochore-targeted motorless CENP-E fragment in cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — purified component reconstitution confirming and extending the 2003 Cell paper finding","pmids":["16144904"],"is_preprint":false},{"year":2012,"finding":"PLK1 phosphorylates a conserved kinetochore attachment regulatory domain (KARD) in BUBR1, which then directly recruits PP2A-B56α phosphatase to kinetochores. This PP2A-B56α counters excessive Aurora B activity at kinetochores to stabilize kinetochore-microtubule attachments; removal of BUBR1 or PLK1 inhibition reduces PP2A-B56α kinetochore binding and elevates Aurora B substrate phosphorylation.","method":"Domain deletion and phospho-site mutagenesis; co-immunoprecipitation of BUBR1 with PP2A-B56α; Aurora B substrate phosphorylation assays; rescue experiments in mitotic cells","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (mutagenesis, reciprocal co-IP, kinase assays, rescue), replicated by two independent papers (PMID 23079597 and 23345399)","pmids":["23079597"],"is_preprint":false},{"year":2013,"finding":"BubR1 directly binds the B56 family of PP2A regulatory subunits through a conserved motif phosphorylated by Cdk1 and Plk1; two conserved hydrophobic residues surrounding the Ser670 Cdk1 site are required for B56 binding. BubR1 targets a pool of B56-PP2A to kinetochores to counteract Aurora B kinase activity at improperly attached kinetochores.","method":"Direct binding assays; phospho-site mutagenesis; co-immunoprecipitation; kinetochore localization assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding confirmed with mutagenesis, independently replicating the KARD/PP2A mechanism from PMID 23079597","pmids":["23345399"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of the PP2A B56–BubR1 complex shows that a conserved BubR1 LxxIxE motif binds to the concave side of B56 pseudo-HEAT repeats (groove between repeats 3 and 4), distant from both the PP2A catalytic C subunit binding surface on B56 and the shugoshin-binding surface, allowing simultaneous binding.","method":"X-ray crystallography; biochemical binding assays","journal":"Protein & cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with biochemical validation, single lab but structure is definitive","pmids":["27350047"],"is_preprint":false},{"year":2012,"finding":"Vertebrate BUBR1 has evolved into an unusual pseudokinase: catalytic motifs are degenerate in many vertebrates, and putative catalysis by human BUBR1 is dispensable for error-free chromosome segregation, whereas residues that interact with ATP are essential for conformational stability. The ancestral KEN box was preserved while the kinase domain underwent parallel subfunctionalization across nine independent gene duplication events.","method":"Comparative genomic analysis; kinase-dead mutant complementation assays in human cells; structural analysis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis-based functional complementation plus evolutionary structural analysis in a single rigorous study","pmids":["22698286"],"is_preprint":false},{"year":2012,"finding":"BubR1 autophosphorylates itself in human cells in a CENP-E-dependent manner at unattached kinetochores; this autophosphorylation is required for full-strength mitotic checkpoint signaling and chromosome alignment. Expressing non-phosphorylatable BubR1 or depleting CENP-E causes metaphase chromosome misalignment and decreased Aurora B-mediated Ndc80 phosphorylation; phosphomimetic BubR1 rescues polar chromosomes in CENP-E-depleted cells.","method":"In vitro kinase assay; phospho-site mutagenesis; CENP-E depletion; live-cell imaging; kinetochore phosphorylation assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay with mutagenesis, multiple orthogonal cellular readouts, single lab","pmids":["22801780"],"is_preprint":false},{"year":2003,"finding":"Aurora B kinase activity is required for kinetochore localization of BubR1, Mad2, and CENP-E; inhibition of Aurora B with ZM447439 prevents rebinding of BubR1 to metaphase kinetochores after reduction of centromeric tension and prevents Aurora B-mediated phosphorylation of BubR1 on entry into mitosis. BubR1 is also required for chromosome alignment independent of its spindle checkpoint role.","method":"Small molecule Aurora kinase inhibitor (ZM447439); RNAi knockdown; immunofluorescence; live-cell imaging","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological inhibition plus RNAi, reciprocal localization and phosphorylation assays, replicated across multiple cell biology approaches","pmids":["12719470"],"is_preprint":false},{"year":2004,"finding":"BubR1 depletion in human cells prevents stable chromosome-spindle attachments; this can be rescued by Aurora kinase inhibition. BubR1 loss increases phosphorylation of the kinetochore-specific Aurora substrate CENP-A, indicating BubR1 links regulation of kinetochore-microtubule attachment stability to Aurora kinase activity.","method":"siRNA depletion; Aurora kinase inhibition; immunofluorescence; live-cell imaging; CENP-A phosphorylation assay","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — siRNA + pharmacological rescue + substrate phosphorylation, multiple orthogonal readouts in single study","pmids":["15592459"],"is_preprint":false},{"year":2010,"finding":"Functional dissection of human BubR1 demonstrates that SAC and chromosome attachment functions are separable: mutation of five proline-directed serine phosphorylation sites abolishes chromosome attachment without affecting SAC; mutation of KEN boxes impairs SAC without affecting congression. The N-terminal KEN box (not the C-terminal) binds Cdc20; the GLEBS motif is strictly required for Bub3 interaction, kinetochore localization, and both SAC and congression functions.","method":"In vivo phospho-site identification by mass spectrometry; site-directed mutagenesis; co-immunoprecipitation; live-cell imaging; mitotic timing assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — MS-identified phospho-sites + mutagenesis + co-IP + multiple functional readouts, systematic domain dissection","pmids":["20016069"],"is_preprint":false},{"year":2011,"finding":"BUBR1 directly interacts with closed MAD2 (C-MAD2) through Arg133 and Gln134 of C-MAD2, and this BUBR1-C-MAD2 interaction is essential for MCC-mediated inhibition of APC/C. The same C-MAD2 residues are required for MAD2 dimerization and p31(comet) binding, suggesting the MAD2 αC helix is central to checkpoint activation and silencing.","method":"Co-immunoprecipitation; mutagenesis; in vitro APC/C inhibition assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP with mutagenesis and in vitro functional APC/C assay","pmids":["21525009"],"is_preprint":false},{"year":2014,"finding":"BubR1 protein abundance declines with age due to decreased NAD+ levels and reduced SIRT2 deacetylase activity; SIRT2 maintains BubR1 by deacetylating lysine 668, which is counteracted by the acetyltransferase CBP. NMN treatment or SIRT2 overexpression restores BubR1 levels in vivo and extends median lifespan of BubR1 hypomorphic mice.","method":"SIRT2 overexpression mice; NMN treatment in vivo; acetylation-site mutagenesis; CBP identification; co-immunoprecipitation; lifespan analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — acetylation site identified with mutagenesis, writer (CBP) and eraser (SIRT2) both characterized, in vivo rescue with NMN and transgenic overexpression","pmids":["24825348"],"is_preprint":false},{"year":2007,"finding":"PLK1 phosphorylates BubR1 in vitro at two consensus Plk1 sites within the kinase domain during prometaphase; phosphomimetic BubR1 (2E) rescues chromosome alignment defects in BubR1-deficient cells, while unphosphorylatable BubR1 (2A) does not; phosphomimetic BubR1 also rescues alignment when Plk1 is co-depleted, placing PLK1-mediated BubR1 phosphorylation in the chromosome alignment pathway.","method":"In vitro kinase assay (Plk1 phosphorylates BubR1); siRNA depletion; phospho-mutant rescue experiments; co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay with mutagenesis, functional rescue experiments, epistasis established","pmids":["17376779"],"is_preprint":false},{"year":2007,"finding":"BubR1 directly associates with APC (adenomatous polyposis coli) and EB1 in Xenopus egg extracts; using purified components BubR1 directly phosphorylates APC and forms a ternary complex with APC and microtubules; immunodepletion of BubR1 from extracts disrupts metaphase chromosome alignment, which requires BubR1 kinase activity.","method":"Co-immunoprecipitation; immunodepletion from Xenopus extracts; in vitro kinase assay with purified components; ternary complex formation assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — purified component reconstitution plus in vitro kinase assay, confirmed in Xenopus extract system","pmids":["17709426"],"is_preprint":false},{"year":2011,"finding":"BubR1 is sumoylated during mitotic progression; lysine 250 is the critical sumoylation site; expression of a sumoylation-deficient BubR1 K250R mutant induces chromosomal missegregation and mitotic delay, demonstrating that sumoylation at K250 is essential for BubR1 function in mitosis.","method":"Ectopic expression; SUMO pulldown; mutagenesis (K250R); immunofluorescence; mitotic timing assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — sumoylation site identified by mutagenesis with functional consequence, single lab","pmids":["22167194"],"is_preprint":false},{"year":2017,"finding":"The BubR1 loop region (distinct from the Bub1 loop) is essential for SAC function; BubR1 loop mutants bind Bub3 and are incorporated into MCC in vitro but have reduced ability to inhibit APC/C, suggesting BubR1:Bub3 requires phosphorylation to recognize and inhibit APC/C — directing Bub3 to distinct phosphorylated targets compared to Bub1.","method":"In vitro APC/C inhibition assay; MCC assembly assay; mutagenesis; SAC functional assays in cells","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution of APC/C inhibition plus mutagenesis plus cellular functional assays","pmids":["28943088"],"is_preprint":false},{"year":2016,"finding":"Two distinct pools of BubR1/Bub3 exist at kinetochores: the major pool depends on direct Bub1/Bub3 binding and is required for chromosome alignment but not SAC; a separate pool binds directly to phosphorylated MELT repeats on KNL1 and is required for efficient incorporation into checkpoint complexes and robust SAC signaling.","method":"Defined BubR1/Bub3 binding mutants; kinetochore localization assays; SAC functional assays; co-immunoprecipitation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — structure-function mutants that uncouple distinct kinetochore pools with specific functional consequences, multiple orthogonal readouts","pmids":["27457023"],"is_preprint":false},{"year":2009,"finding":"In Drosophila, BubR1 kinase activity is required for spindle function (kinetochore fiber organization) but is dispensable for SAC function; the N-terminal KEN box is required for SAC but not spindle function; these two functions are substantially separable from each other and from mitotic timing.","method":"Kinase-dead and KEN-box mutant transgenic Drosophila; genetic epistasis with mad2; chromosome segregation analysis; spindle imaging","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis plus multiple domain mutants in intact organism with multiple phenotypic readouts","pmids":["19951912"],"is_preprint":false},{"year":2015,"finding":"In Drosophila, Bub3-BubR1 complex localizes to broken chromosome fragments (DNA double-strand breaks) in a Bub3-dependent manner; Cdc20 accumulates at DNA breaks in a BubR1 KEN-box-dependent manner; BubR1-dependent local APC/C inhibition around segregating broken chromosomes promotes their faithful segregation.","method":"RNAi depletion; KEN-box mutant analysis; APC/C activity biosensor; live-cell imaging; immunofluorescence","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KEN-box mutagenesis with APC/C biosensor and live imaging, single lab in Drosophila model","pmids":["26553926"],"is_preprint":false},{"year":2017,"finding":"SIRT2-dependent deacetylation of BubR1 at lysine 243 is required for normal meiotic spindle/chromosome organization in mouse oocytes; acetylation-mimetic BubR1-K243Q phenocopies Sirt2-knockdown meiotic defects, and non-acetylatable BubR1-K243R partly rescues meiotic deficits in Sirt2-depleted oocytes and suppresses spindle/chromosome anomalies in aged-mouse oocytes.","method":"Sirt2 depletion by morpholino/siRNA; acetylation-mimetic and non-acetylatable BubR1 mutant microinjection; spindle/chromosome immunofluorescence; aneuploidy scoring","journal":"Aging cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis-based rescue experiments with multiple functional readouts, single lab","pmids":["29067790"],"is_preprint":false},{"year":2014,"finding":"SIRT2 deacetylates BubR1 at lysine 250 both in vitro and in vivo; K250 acetylation during prometaphase inhibits APC/C-dependent proteolysis of BubR1 and regulates anaphase entry timing; SIRT2 knockdown increases BubR1 K250 acetylation.","method":"In vitro deacetylation assay; in vivo acetylation analysis; SIRT2 siRNA knockdown; Western blot of BubR1 levels and APC/C substrates","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo deacetylation assay, single lab, some functional ambiguity noted by authors","pmids":["25285631"],"is_preprint":false},{"year":2005,"finding":"BubR1 contains two distinct functional domains: the N-terminal region including the GLEBS motif is required for spindle checkpoint function through disruption of Bub3 binding; the C-terminal kinase domain is required for chromosome movement/alignment during prometaphase; a kinase-dead mutant prolongs mitosis, indicating the kinase domain regulates chromosome movement independently of the checkpoint.","method":"Deletion and kinase-dead point mutants; HeLa cell transfection; mitotic timing by live imaging; checkpoint assays with nocodazole","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic domain mutagenesis with functional readouts, single lab","pmids":["15907836"],"is_preprint":false},{"year":2020,"finding":"The C-terminal basic helix of BubR1 is necessary (but not sufficient) for CENP-E interaction; a minimal acidic patch on the kinetochore-targeting domain of CENP-E is also essential. BubR1 is required for CENP-E recruitment to kinetochores, and this BubR1-CENP-E axis is critical for alignment of chromosomes that have failed other congression pathways.","method":"Domain mutagenesis; co-immunoprecipitation; kinetochore localization assays; chromosome alignment assays with rescue experiments","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — molecular determinants identified by mutagenesis with reciprocal interaction and functional rescue, single lab","pmids":["32665320"],"is_preprint":false},{"year":2005,"finding":"BubR1 checkpoint function depends on both Bub1 kinase activity and Aurora B kinase activity in a redundant manner (two checkpoint arms converge on the MCC containing BubR1, Bub3, Mad2, Cdc20); MCC binding to APC/C requires an active checkpoint signal and depends on both Bub1 and Aurora B kinase activities.","method":"RNAi depletion of Bub1; Aurora kinase inhibitor ZM447439; co-immunoprecipitation of MCC-APC/C; mitotic arrest assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — double depletion epistasis with co-IP of complex, single lab","pmids":["16046481"],"is_preprint":false},{"year":2006,"finding":"BubR1 physically interacts with PARP-1, identified by affinity pulldown and mass spectrometry and confirmed by reciprocal co-immunoprecipitation; BubR1 deficiency in MEFs compromises retention of intact PARP-1 after DNA damage, suggesting BubR1 participates in DNA damage responses through interaction with PARP-1.","method":"Affinity pulldown coupled with mass spectrometry; reciprocal co-immunoprecipitation; BubR1+/- mouse embryonic fibroblasts; DNA damage assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — MS-identified interaction confirmed by reciprocal co-IP, functional consequence in haploinsufficient cells","pmids":["16449973"],"is_preprint":false},{"year":2003,"finding":"BCSG1 (breast cancer-specific gene 1/gamma-synuclein) physically associates with BubR1 in breast cancer cells (yeast two-hybrid, immunoprecipitation, GST pulldown); BCSG1 overexpression reduces BubR1 protein levels via the proteasome (prevented by MG-132), impairing mitotic checkpoint function.","method":"Yeast two-hybrid; co-immunoprecipitation; GST pulldown; proteasome inhibition with MG-132; Western blot","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — three orthogonal binding methods plus proteasome inhibition, single lab","pmids":["14576821"],"is_preprint":false},{"year":2007,"finding":"hStaf/ZNF143 is required for BUB1B gene transcription; two conserved hStaf/ZNF143-binding sites in the BUB1B promoter are indispensable for promoter activity; CDE-CHR tandem elements in the promoter are essential for G2/M-specific cell-cycle-regulated transcription of BUB1B.","method":"Gel retardation assays; transient expression of mutant BUB1B promoter-reporter constructs; chromatin immunoprecipitation","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus mutagenesis of promoter elements with reporter assays, single lab","pmids":["17478512"],"is_preprint":false},{"year":2005,"finding":"BubR1 transcription is largely controlled by p53; in p53-null mouse cells, BubR1 expression is low and the checkpoint response to microtubule toxin is compromised; restoration of BubR1 in late-passage p53-/- cells restores checkpoint function and suppresses centrosome amplification.","method":"Microarray analysis; RT-PCR; Western blot; checkpoint assays in p53-/- cells with BubR1 re-expression","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — p53 identified as transcriptional regulator with functional rescue, single lab","pmids":["15870277"],"is_preprint":false},{"year":2008,"finding":"BubR1 haploinsufficiency causes premature sister-chromatid separation (PCS) in human cells; gradual reduction of BubR1 via shRNA reveals a dosage-dependent relationship: PCS is detected at all levels of reduction, whereas aneuploidy is clearly detected only when residual BubR1 is below 50%.","method":"Stable shRNA-transduced HeLa cells expressing gradient levels of BubR1; chromosome spreading; flow cytometry","journal":"Human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative dose-response analysis with defined residual protein levels, single lab","pmids":["18932004"],"is_preprint":false},{"year":2010,"finding":"BubR1 localizes to kinetochores in mouse oocytes from GVBD to prometaphase I (co-localizing with PLK1) and redistributes away from kinetochores at metaphase I; spindle disruption relocalizes BubR1 to kinetochores. BubR1 depletion compromises kinetochore-microtubule attachments in meiosis I and abrogates the nocodazole-induced M I arrest.","method":"Immunofluorescence; BubR1 depletion by morpholino; dominant-negative overexpression; live-cell imaging; nocodazole checkpoint assay","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — depletion plus dominant-negative with multiple phenotypic readouts, single lab","pmids":["20237433"],"is_preprint":false},{"year":2012,"finding":"FOXM1 transcriptionally regulates BUB1B expression by binding to and activating the BUB1B promoter, as demonstrated by chromatin immunoprecipitation; the FOXM1/BUB1B pathway promotes tumor cell growth and survival in rhabdomyosarcoma.","method":"Chromatin immunoprecipitation; shRNA knockdown; in vivo tumor growth assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP confirms direct promoter binding, supported by functional knockdown, single lab","pmids":["23002205"],"is_preprint":false},{"year":2021,"finding":"Phosphorylated ATM interacts with BUB1B/BUBR1 after ionizing radiation; cells with aberrant BUB1B expression dominantly exploit mutagenic NHEJ for DNA repair in an ATM-dependent manner; FOXM1 was identified as a transcription factor causing increased BUB1B expression in CRT-recurrent bladder cancer clones.","method":"Co-immunoprecipitation of phospho-ATM with BUB1B; CRISPR/Cas9 DNA repair pathway analysis; ATM inhibitor experiments; ChIP for FOXM1","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus pharmacological inhibition and CRISPR-based pathway analysis, single lab","pmids":["34545188"],"is_preprint":false}],"current_model":"BubR1 (BUB1B) is a multifunctional pseudokinase/checkpoint scaffold that (1) inhibits APC/C-Cdc20 as a core component of the Mitotic Checkpoint Complex (MCC) via its KEN boxes and direct interaction with closed MAD2; (2) is activated as a kinase by direct binding to the motor CENP-E at unattached kinetochores and silenced when CENP-E captures spindle microtubules in a ternary BubR1-CENP-E-microtubule complex; (3) recruits PP2A-B56 phosphatase to kinetochores through a PLK1/CDK1-phosphorylated KARD/LxxIxE motif to counteract Aurora B and stabilize kinetochore-microtubule attachments; (4) recruits CENP-E to kinetochores via its C-terminal basic helix to facilitate chromosome alignment; (5) is regulated by post-translational modifications including PLK1 phosphorylation (promoting chromosome alignment), SIRT2-dependent deacetylation at K668 (controlling protein stability) and K250/K243 (regulating mitotic timing and meiotic fidelity), and SUMO modification at K250 (required for accurate chromosome segregation); and (6) has its transcription regulated by p53 and hStaf/ZNF143 and its abundance maintained by NAD⁺/SIRT2 signaling."},"narrative":{"mechanistic_narrative":"BUB1B (BubR1) is a dual-function mitotic regulator that both enforces the spindle assembly checkpoint (SAC) and promotes chromosome alignment, with these two activities residing in genetically separable modules [PMID:20016069, PMID:19951912, PMID:15907836]. As a core component of the Mitotic Checkpoint Complex, BubR1 inhibits APC/C-Cdc20: its N-terminal KEN box binds Cdc20 and it directly engages closed MAD2 through MAD2 residues Arg133/Gln134, while the BubR1:Bub3 module requires phosphorylation-dependent recognition of its targets to inhibit APC/C [PMID:20016069, PMID:21525009, PMID:28943088]. Kinetochore recruitment of BubR1/Bub3 occurs through two pools — a Bub1/Bub3-dependent pool driving alignment and a separate pool binding phosphorylated MELT repeats on KNL1 that supports robust checkpoint signaling [PMID:27457023]. Beyond checkpoint control, BubR1 stabilizes kinetochore-microtubule attachments by recruiting PP2A-B56 phosphatase: PLK1/CDK1 phosphorylation of the conserved KARD/LxxIxE motif (around Ser670) creates a docking site that binds the concave groove of B56 pseudo-HEAT repeats, delivering PP2A to counteract Aurora B activity at improperly attached kinetochores [PMID:23079597, PMID:23345399, PMID:27350047]. BubR1 also recruits CENP-E to kinetochores via its C-terminal basic helix to rescue chromosomes that fail other congression pathways, and CENP-E reciprocally controls BubR1 catalytic state — activating it at unattached kinetochores and silencing it upon microtubule capture in a ternary BubR1-CENP-E-microtubule complex [PMID:12859900, PMID:16144904, PMID:32665320]. Although vertebrate BubR1 has degenerated into a pseudokinase whose catalysis is dispensable for error-free segregation, its ATP-binding residues remain essential for conformational stability [PMID:22698286]. BubR1 abundance and activity are set by transcriptional inputs from p53 and hStaf/ZNF143 and by post-translational control, including SIRT2-dependent deacetylation that maintains protein stability and segregation fidelity [PMID:24825348, PMID:17478512, PMID:15870277]. BubR1 haploinsufficiency causes premature sister-chromatid separation and, at deeper loss, aneuploidy [PMID:18932004].","teleology":[{"year":2003,"claim":"Established how BubR1 catalytic state is coupled to the physical state of the kinetochore, answering how attachment status is transduced into a checkpoint signal.","evidence":"In vitro reconstitution with purified BubR1, CENP-E, and microtubules plus Xenopus egg extract depletion/add-back","pmids":["12859900"],"confidence":"High","gaps":["Did not resolve which BubR1 substrates are phosphorylated upon activation","Vertebrate pseudokinase status later complicated the kinase interpretation"]},{"year":2003,"claim":"Placed BubR1 downstream of Aurora B for kinetochore localization and showed BubR1 has an alignment role beyond the checkpoint.","evidence":"Aurora B inhibitor ZM447439, RNAi, and live-cell imaging in human cells","pmids":["12719470"],"confidence":"High","gaps":["Mechanism linking Aurora B activity to BubR1 retention under tension not defined","Did not separate checkpoint from attachment contributions molecularly"]},{"year":2004,"claim":"Demonstrated BubR1 stabilizes kinetochore-microtubule attachments by limiting Aurora B substrate phosphorylation, foreshadowing a phosphatase-counterbalancing role.","evidence":"siRNA depletion with Aurora inhibition rescue and CENP-A phosphorylation readout in human cells","pmids":["15592459"],"confidence":"High","gaps":["Did not identify the phosphatase BubR1 recruits","Direct vs indirect effect on Aurora B unresolved at this stage"]},{"year":2005,"claim":"Resolved BubR1 into separable N-terminal checkpoint (GLEBS/Bub3) and C-terminal kinase-domain alignment modules.","evidence":"Domain deletion and kinase-dead mutants with mitotic timing in HeLa cells","pmids":["15907836"],"confidence":"Medium","gaps":["Single lab","Kinase-dependence of alignment later reframed by pseudokinase findings"]},{"year":2005,"claim":"Identified p53 as a transcriptional regulator of BubR1, linking BubR1 dosage to genome stability.","evidence":"Microarray/RT-PCR and re-expression rescue in p53-null mouse cells","pmids":["15870277"],"confidence":"Medium","gaps":["Direct vs indirect transcriptional control not fully established","Single lab"]},{"year":2005,"claim":"Showed BubR1-containing MCC binding to APC/C requires convergent Bub1 and Aurora B kinase signals.","evidence":"Bub1 RNAi plus Aurora inhibitor with MCC-APC/C co-IP in human cells","pmids":["16046481"],"confidence":"Medium","gaps":["Redundancy mechanism between the two kinase arms not defined","Single lab"]},{"year":2006,"claim":"Linked BubR1 to the DNA damage response through a physical interaction with PARP-1.","evidence":"Affinity-MS and reciprocal co-IP with damage assays in BubR1+/- MEFs","pmids":["16449973"],"confidence":"Medium","gaps":["Functional significance of PARP-1 binding for repair not mechanistically resolved","Single lab"]},{"year":2007,"claim":"Placed PLK1 phosphorylation of BubR1 in the chromosome alignment pathway.","evidence":"In vitro Plk1 kinase assay, phospho-mutant rescue, and epistasis in BubR1-deficient cells","pmids":["17376779"],"confidence":"High","gaps":["Downstream effector of these phospho-sites not identified at this stage","Relationship to later KARD/PP2A motif not yet drawn"]},{"year":2007,"claim":"Identified hStaf/ZNF143 and cell-cycle promoter elements driving G2/M-specific BUB1B transcription.","evidence":"Gel shift, promoter-reporter mutagenesis, and ChIP","pmids":["17478512"],"confidence":"Medium","gaps":["Single lab","Interplay with p53 control not addressed"]},{"year":2010,"claim":"Provided a systematic separation-of-function map distinguishing SAC (KEN/GLEBS) from attachment (proline-directed phospho-sites).","evidence":"MS phospho-site mapping, mutagenesis, co-IP, and live imaging in human cells","pmids":["20016069"],"confidence":"High","gaps":["Effectors of the proline-directed sites not all identified","How GLEBS/Bub3 binding triggers kinetochore loading not structurally resolved"]},{"year":2011,"claim":"Defined the molecular basis of BubR1 engagement with closed MAD2 essential for MCC-mediated APC/C inhibition.","evidence":"Co-IP, MAD2 mutagenesis, and in vitro APC/C inhibition assays","pmids":["21525009"],"confidence":"High","gaps":["How MAD2 alpha-C helix coordinates activation vs silencing not fully resolved"]},{"year":2012,"claim":"Resolved the phosphatase BubR1 recruits, defining the PLK1-phosphorylated KARD-PP2A-B56 axis that counters Aurora B at kinetochores.","evidence":"Domain/phospho-mutagenesis, reciprocal co-IP, Aurora B substrate and rescue assays (independently replicated)","pmids":["23079597","23345399"],"confidence":"High","gaps":["Spatial regulation of PP2A delivery during attachment maturation not fully timed"]},{"year":2012,"claim":"Reframed vertebrate BubR1 as a pseudokinase whose catalysis is dispensable but whose ATP-binding residues stabilize conformation.","evidence":"Comparative genomics with kinase-dead complementation in human cells","pmids":["22698286"],"confidence":"High","gaps":["Reconciliation with earlier kinase-activity reports across species incomplete"]},{"year":2012,"claim":"Showed CENP-E-dependent BubR1 autophosphorylation supports full checkpoint strength and alignment in human cells.","evidence":"In vitro kinase assay, phospho-mutants, CENP-E depletion, and live imaging","pmids":["22801780"],"confidence":"High","gaps":["Difficult to reconcile with pseudokinase model in same year","Relevant in vivo substrates not pinned down"]},{"year":2014,"claim":"Established NAD+/SIRT2 deacetylation at K668 as a determinant of BubR1 stability with organismal lifespan consequences.","evidence":"Acetylation-site mutagenesis, CBP identification, NMN and SIRT2-overexpression in mice with lifespan analysis","pmids":["24825348"],"confidence":"High","gaps":["How K668 acetylation triggers turnover mechanistically not fully defined"]},{"year":2016,"claim":"Provided a crystal structure showing the BubR1 LxxIxE motif binds the B56 concave groove without occluding catalytic or shugoshin surfaces.","evidence":"X-ray crystallography with biochemical binding assays","pmids":["27350047"],"confidence":"High","gaps":["Single lab","Dynamics of phospho-dependent binding in cells not captured"]},{"year":2016,"claim":"Distinguished two kinetochore BubR1/Bub3 pools with separable alignment vs checkpoint roles.","evidence":"Binding-mutant dissection, kinetochore localization, SAC assays, and co-IP","pmids":["27457023"],"confidence":"High","gaps":["Quantitative partitioning between pools during mitosis not measured"]},{"year":2017,"claim":"Identified a BubR1-specific loop required for APC/C inhibition, showing BubR1:Bub3 needs phosphorylation to target APC/C distinctly from Bub1.","evidence":"In vitro APC/C inhibition and MCC assembly with mutagenesis and cellular SAC assays","pmids":["28943088"],"confidence":"High","gaps":["Identity of the phosphorylated APC/C target 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age-related cellular changes in BubR1 progeroid mice.","date":"2019","source":"Aging cell","url":"https://pubmed.ncbi.nlm.nih.gov/30609266","citation_count":17,"is_preprint":false},{"pmid":"25256220","id":"PMC_25256220","title":"How chromosome mis-segregation leads to cancer: lessons from BubR1 mouse models.","date":"2014","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/25256220","citation_count":16,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48054,"output_tokens":8129,"usd":0.133048,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17556,"output_tokens":5133,"usd":0.108052,"stage2_stop_reason":"end_turn"},"total_usd":0.2411,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"CENP-E directly activates BubR1 kinase activity at kinetochores using purified components and Xenopus egg extracts; microtubule capture by the CENP-E motor domain silences BubR1 kinase activity in a ternary BubR1-CENP-E-microtubule complex, establishing CENP-E as the signal transducing linker that both activates and silences BubR1-dependent mitotic checkpoint signaling.\",\n      \"method\": \"In vitro reconstitution with purified BubR1, CENP-E, and microtubules; Xenopus egg extract immunodepletion and antibody-addition experiments\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with purified components, replicated across two independent experimental systems (extracts + purified proteins) in a single rigorous study\",\n      \"pmids\": [\"12859900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Microtubule capture by CENP-E silences BubR1 kinase activity: a motorless fragment of CENP-E constitutively activates BubR1 at kinetochores producing checkpoint signaling not silenced by spindle capture or tension, whereas the motor domain of CENP-E silences BubR1 kinase in a ternary BubR1-CENP-E-microtubule complex in vitro.\",\n      \"method\": \"Biochemical reconstitution with purified BubR1, microtubules, and CENP-E; kinetochore-targeted motorless CENP-E fragment in cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — purified component reconstitution confirming and extending the 2003 Cell paper finding\",\n      \"pmids\": [\"16144904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PLK1 phosphorylates a conserved kinetochore attachment regulatory domain (KARD) in BUBR1, which then directly recruits PP2A-B56α phosphatase to kinetochores. This PP2A-B56α counters excessive Aurora B activity at kinetochores to stabilize kinetochore-microtubule attachments; removal of BUBR1 or PLK1 inhibition reduces PP2A-B56α kinetochore binding and elevates Aurora B substrate phosphorylation.\",\n      \"method\": \"Domain deletion and phospho-site mutagenesis; co-immunoprecipitation of BUBR1 with PP2A-B56α; Aurora B substrate phosphorylation assays; rescue experiments in mitotic cells\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (mutagenesis, reciprocal co-IP, kinase assays, rescue), replicated by two independent papers (PMID 23079597 and 23345399)\",\n      \"pmids\": [\"23079597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"BubR1 directly binds the B56 family of PP2A regulatory subunits through a conserved motif phosphorylated by Cdk1 and Plk1; two conserved hydrophobic residues surrounding the Ser670 Cdk1 site are required for B56 binding. BubR1 targets a pool of B56-PP2A to kinetochores to counteract Aurora B kinase activity at improperly attached kinetochores.\",\n      \"method\": \"Direct binding assays; phospho-site mutagenesis; co-immunoprecipitation; kinetochore localization assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding confirmed with mutagenesis, independently replicating the KARD/PP2A mechanism from PMID 23079597\",\n      \"pmids\": [\"23345399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of the PP2A B56–BubR1 complex shows that a conserved BubR1 LxxIxE motif binds to the concave side of B56 pseudo-HEAT repeats (groove between repeats 3 and 4), distant from both the PP2A catalytic C subunit binding surface on B56 and the shugoshin-binding surface, allowing simultaneous binding.\",\n      \"method\": \"X-ray crystallography; biochemical binding assays\",\n      \"journal\": \"Protein & cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with biochemical validation, single lab but structure is definitive\",\n      \"pmids\": [\"27350047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vertebrate BUBR1 has evolved into an unusual pseudokinase: catalytic motifs are degenerate in many vertebrates, and putative catalysis by human BUBR1 is dispensable for error-free chromosome segregation, whereas residues that interact with ATP are essential for conformational stability. The ancestral KEN box was preserved while the kinase domain underwent parallel subfunctionalization across nine independent gene duplication events.\",\n      \"method\": \"Comparative genomic analysis; kinase-dead mutant complementation assays in human cells; structural analysis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis-based functional complementation plus evolutionary structural analysis in a single rigorous study\",\n      \"pmids\": [\"22698286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"BubR1 autophosphorylates itself in human cells in a CENP-E-dependent manner at unattached kinetochores; this autophosphorylation is required for full-strength mitotic checkpoint signaling and chromosome alignment. Expressing non-phosphorylatable BubR1 or depleting CENP-E causes metaphase chromosome misalignment and decreased Aurora B-mediated Ndc80 phosphorylation; phosphomimetic BubR1 rescues polar chromosomes in CENP-E-depleted cells.\",\n      \"method\": \"In vitro kinase assay; phospho-site mutagenesis; CENP-E depletion; live-cell imaging; kinetochore phosphorylation assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay with mutagenesis, multiple orthogonal cellular readouts, single lab\",\n      \"pmids\": [\"22801780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Aurora B kinase activity is required for kinetochore localization of BubR1, Mad2, and CENP-E; inhibition of Aurora B with ZM447439 prevents rebinding of BubR1 to metaphase kinetochores after reduction of centromeric tension and prevents Aurora B-mediated phosphorylation of BubR1 on entry into mitosis. BubR1 is also required for chromosome alignment independent of its spindle checkpoint role.\",\n      \"method\": \"Small molecule Aurora kinase inhibitor (ZM447439); RNAi knockdown; immunofluorescence; live-cell imaging\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological inhibition plus RNAi, reciprocal localization and phosphorylation assays, replicated across multiple cell biology approaches\",\n      \"pmids\": [\"12719470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"BubR1 depletion in human cells prevents stable chromosome-spindle attachments; this can be rescued by Aurora kinase inhibition. BubR1 loss increases phosphorylation of the kinetochore-specific Aurora substrate CENP-A, indicating BubR1 links regulation of kinetochore-microtubule attachment stability to Aurora kinase activity.\",\n      \"method\": \"siRNA depletion; Aurora kinase inhibition; immunofluorescence; live-cell imaging; CENP-A phosphorylation assay\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA + pharmacological rescue + substrate phosphorylation, multiple orthogonal readouts in single study\",\n      \"pmids\": [\"15592459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Functional dissection of human BubR1 demonstrates that SAC and chromosome attachment functions are separable: mutation of five proline-directed serine phosphorylation sites abolishes chromosome attachment without affecting SAC; mutation of KEN boxes impairs SAC without affecting congression. The N-terminal KEN box (not the C-terminal) binds Cdc20; the GLEBS motif is strictly required for Bub3 interaction, kinetochore localization, and both SAC and congression functions.\",\n      \"method\": \"In vivo phospho-site identification by mass spectrometry; site-directed mutagenesis; co-immunoprecipitation; live-cell imaging; mitotic timing assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — MS-identified phospho-sites + mutagenesis + co-IP + multiple functional readouts, systematic domain dissection\",\n      \"pmids\": [\"20016069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"BUBR1 directly interacts with closed MAD2 (C-MAD2) through Arg133 and Gln134 of C-MAD2, and this BUBR1-C-MAD2 interaction is essential for MCC-mediated inhibition of APC/C. The same C-MAD2 residues are required for MAD2 dimerization and p31(comet) binding, suggesting the MAD2 αC helix is central to checkpoint activation and silencing.\",\n      \"method\": \"Co-immunoprecipitation; mutagenesis; in vitro APC/C inhibition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP with mutagenesis and in vitro functional APC/C assay\",\n      \"pmids\": [\"21525009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"BubR1 protein abundance declines with age due to decreased NAD+ levels and reduced SIRT2 deacetylase activity; SIRT2 maintains BubR1 by deacetylating lysine 668, which is counteracted by the acetyltransferase CBP. NMN treatment or SIRT2 overexpression restores BubR1 levels in vivo and extends median lifespan of BubR1 hypomorphic mice.\",\n      \"method\": \"SIRT2 overexpression mice; NMN treatment in vivo; acetylation-site mutagenesis; CBP identification; co-immunoprecipitation; lifespan analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — acetylation site identified with mutagenesis, writer (CBP) and eraser (SIRT2) both characterized, in vivo rescue with NMN and transgenic overexpression\",\n      \"pmids\": [\"24825348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PLK1 phosphorylates BubR1 in vitro at two consensus Plk1 sites within the kinase domain during prometaphase; phosphomimetic BubR1 (2E) rescues chromosome alignment defects in BubR1-deficient cells, while unphosphorylatable BubR1 (2A) does not; phosphomimetic BubR1 also rescues alignment when Plk1 is co-depleted, placing PLK1-mediated BubR1 phosphorylation in the chromosome alignment pathway.\",\n      \"method\": \"In vitro kinase assay (Plk1 phosphorylates BubR1); siRNA depletion; phospho-mutant rescue experiments; co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay with mutagenesis, functional rescue experiments, epistasis established\",\n      \"pmids\": [\"17376779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"BubR1 directly associates with APC (adenomatous polyposis coli) and EB1 in Xenopus egg extracts; using purified components BubR1 directly phosphorylates APC and forms a ternary complex with APC and microtubules; immunodepletion of BubR1 from extracts disrupts metaphase chromosome alignment, which requires BubR1 kinase activity.\",\n      \"method\": \"Co-immunoprecipitation; immunodepletion from Xenopus extracts; in vitro kinase assay with purified components; ternary complex formation assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — purified component reconstitution plus in vitro kinase assay, confirmed in Xenopus extract system\",\n      \"pmids\": [\"17709426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"BubR1 is sumoylated during mitotic progression; lysine 250 is the critical sumoylation site; expression of a sumoylation-deficient BubR1 K250R mutant induces chromosomal missegregation and mitotic delay, demonstrating that sumoylation at K250 is essential for BubR1 function in mitosis.\",\n      \"method\": \"Ectopic expression; SUMO pulldown; mutagenesis (K250R); immunofluorescence; mitotic timing assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — sumoylation site identified by mutagenesis with functional consequence, single lab\",\n      \"pmids\": [\"22167194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The BubR1 loop region (distinct from the Bub1 loop) is essential for SAC function; BubR1 loop mutants bind Bub3 and are incorporated into MCC in vitro but have reduced ability to inhibit APC/C, suggesting BubR1:Bub3 requires phosphorylation to recognize and inhibit APC/C — directing Bub3 to distinct phosphorylated targets compared to Bub1.\",\n      \"method\": \"In vitro APC/C inhibition assay; MCC assembly assay; mutagenesis; SAC functional assays in cells\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution of APC/C inhibition plus mutagenesis plus cellular functional assays\",\n      \"pmids\": [\"28943088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Two distinct pools of BubR1/Bub3 exist at kinetochores: the major pool depends on direct Bub1/Bub3 binding and is required for chromosome alignment but not SAC; a separate pool binds directly to phosphorylated MELT repeats on KNL1 and is required for efficient incorporation into checkpoint complexes and robust SAC signaling.\",\n      \"method\": \"Defined BubR1/Bub3 binding mutants; kinetochore localization assays; SAC functional assays; co-immunoprecipitation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — structure-function mutants that uncouple distinct kinetochore pools with specific functional consequences, multiple orthogonal readouts\",\n      \"pmids\": [\"27457023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Drosophila, BubR1 kinase activity is required for spindle function (kinetochore fiber organization) but is dispensable for SAC function; the N-terminal KEN box is required for SAC but not spindle function; these two functions are substantially separable from each other and from mitotic timing.\",\n      \"method\": \"Kinase-dead and KEN-box mutant transgenic Drosophila; genetic epistasis with mad2; chromosome segregation analysis; spindle imaging\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis plus multiple domain mutants in intact organism with multiple phenotypic readouts\",\n      \"pmids\": [\"19951912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In Drosophila, Bub3-BubR1 complex localizes to broken chromosome fragments (DNA double-strand breaks) in a Bub3-dependent manner; Cdc20 accumulates at DNA breaks in a BubR1 KEN-box-dependent manner; BubR1-dependent local APC/C inhibition around segregating broken chromosomes promotes their faithful segregation.\",\n      \"method\": \"RNAi depletion; KEN-box mutant analysis; APC/C activity biosensor; live-cell imaging; immunofluorescence\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KEN-box mutagenesis with APC/C biosensor and live imaging, single lab in Drosophila model\",\n      \"pmids\": [\"26553926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIRT2-dependent deacetylation of BubR1 at lysine 243 is required for normal meiotic spindle/chromosome organization in mouse oocytes; acetylation-mimetic BubR1-K243Q phenocopies Sirt2-knockdown meiotic defects, and non-acetylatable BubR1-K243R partly rescues meiotic deficits in Sirt2-depleted oocytes and suppresses spindle/chromosome anomalies in aged-mouse oocytes.\",\n      \"method\": \"Sirt2 depletion by morpholino/siRNA; acetylation-mimetic and non-acetylatable BubR1 mutant microinjection; spindle/chromosome immunofluorescence; aneuploidy scoring\",\n      \"journal\": \"Aging cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis-based rescue experiments with multiple functional readouts, single lab\",\n      \"pmids\": [\"29067790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIRT2 deacetylates BubR1 at lysine 250 both in vitro and in vivo; K250 acetylation during prometaphase inhibits APC/C-dependent proteolysis of BubR1 and regulates anaphase entry timing; SIRT2 knockdown increases BubR1 K250 acetylation.\",\n      \"method\": \"In vitro deacetylation assay; in vivo acetylation analysis; SIRT2 siRNA knockdown; Western blot of BubR1 levels and APC/C substrates\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo deacetylation assay, single lab, some functional ambiguity noted by authors\",\n      \"pmids\": [\"25285631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"BubR1 contains two distinct functional domains: the N-terminal region including the GLEBS motif is required for spindle checkpoint function through disruption of Bub3 binding; the C-terminal kinase domain is required for chromosome movement/alignment during prometaphase; a kinase-dead mutant prolongs mitosis, indicating the kinase domain regulates chromosome movement independently of the checkpoint.\",\n      \"method\": \"Deletion and kinase-dead point mutants; HeLa cell transfection; mitotic timing by live imaging; checkpoint assays with nocodazole\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic domain mutagenesis with functional readouts, single lab\",\n      \"pmids\": [\"15907836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The C-terminal basic helix of BubR1 is necessary (but not sufficient) for CENP-E interaction; a minimal acidic patch on the kinetochore-targeting domain of CENP-E is also essential. BubR1 is required for CENP-E recruitment to kinetochores, and this BubR1-CENP-E axis is critical for alignment of chromosomes that have failed other congression pathways.\",\n      \"method\": \"Domain mutagenesis; co-immunoprecipitation; kinetochore localization assays; chromosome alignment assays with rescue experiments\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — molecular determinants identified by mutagenesis with reciprocal interaction and functional rescue, single lab\",\n      \"pmids\": [\"32665320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"BubR1 checkpoint function depends on both Bub1 kinase activity and Aurora B kinase activity in a redundant manner (two checkpoint arms converge on the MCC containing BubR1, Bub3, Mad2, Cdc20); MCC binding to APC/C requires an active checkpoint signal and depends on both Bub1 and Aurora B kinase activities.\",\n      \"method\": \"RNAi depletion of Bub1; Aurora kinase inhibitor ZM447439; co-immunoprecipitation of MCC-APC/C; mitotic arrest assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — double depletion epistasis with co-IP of complex, single lab\",\n      \"pmids\": [\"16046481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"BubR1 physically interacts with PARP-1, identified by affinity pulldown and mass spectrometry and confirmed by reciprocal co-immunoprecipitation; BubR1 deficiency in MEFs compromises retention of intact PARP-1 after DNA damage, suggesting BubR1 participates in DNA damage responses through interaction with PARP-1.\",\n      \"method\": \"Affinity pulldown coupled with mass spectrometry; reciprocal co-immunoprecipitation; BubR1+/- mouse embryonic fibroblasts; DNA damage assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — MS-identified interaction confirmed by reciprocal co-IP, functional consequence in haploinsufficient cells\",\n      \"pmids\": [\"16449973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"BCSG1 (breast cancer-specific gene 1/gamma-synuclein) physically associates with BubR1 in breast cancer cells (yeast two-hybrid, immunoprecipitation, GST pulldown); BCSG1 overexpression reduces BubR1 protein levels via the proteasome (prevented by MG-132), impairing mitotic checkpoint function.\",\n      \"method\": \"Yeast two-hybrid; co-immunoprecipitation; GST pulldown; proteasome inhibition with MG-132; Western blot\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — three orthogonal binding methods plus proteasome inhibition, single lab\",\n      \"pmids\": [\"14576821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"hStaf/ZNF143 is required for BUB1B gene transcription; two conserved hStaf/ZNF143-binding sites in the BUB1B promoter are indispensable for promoter activity; CDE-CHR tandem elements in the promoter are essential for G2/M-specific cell-cycle-regulated transcription of BUB1B.\",\n      \"method\": \"Gel retardation assays; transient expression of mutant BUB1B promoter-reporter constructs; chromatin immunoprecipitation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus mutagenesis of promoter elements with reporter assays, single lab\",\n      \"pmids\": [\"17478512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"BubR1 transcription is largely controlled by p53; in p53-null mouse cells, BubR1 expression is low and the checkpoint response to microtubule toxin is compromised; restoration of BubR1 in late-passage p53-/- cells restores checkpoint function and suppresses centrosome amplification.\",\n      \"method\": \"Microarray analysis; RT-PCR; Western blot; checkpoint assays in p53-/- cells with BubR1 re-expression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — p53 identified as transcriptional regulator with functional rescue, single lab\",\n      \"pmids\": [\"15870277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"BubR1 haploinsufficiency causes premature sister-chromatid separation (PCS) in human cells; gradual reduction of BubR1 via shRNA reveals a dosage-dependent relationship: PCS is detected at all levels of reduction, whereas aneuploidy is clearly detected only when residual BubR1 is below 50%.\",\n      \"method\": \"Stable shRNA-transduced HeLa cells expressing gradient levels of BubR1; chromosome spreading; flow cytometry\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative dose-response analysis with defined residual protein levels, single lab\",\n      \"pmids\": [\"18932004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"BubR1 localizes to kinetochores in mouse oocytes from GVBD to prometaphase I (co-localizing with PLK1) and redistributes away from kinetochores at metaphase I; spindle disruption relocalizes BubR1 to kinetochores. BubR1 depletion compromises kinetochore-microtubule attachments in meiosis I and abrogates the nocodazole-induced M I arrest.\",\n      \"method\": \"Immunofluorescence; BubR1 depletion by morpholino; dominant-negative overexpression; live-cell imaging; nocodazole checkpoint assay\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — depletion plus dominant-negative with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"20237433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FOXM1 transcriptionally regulates BUB1B expression by binding to and activating the BUB1B promoter, as demonstrated by chromatin immunoprecipitation; the FOXM1/BUB1B pathway promotes tumor cell growth and survival in rhabdomyosarcoma.\",\n      \"method\": \"Chromatin immunoprecipitation; shRNA knockdown; in vivo tumor growth assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP confirms direct promoter binding, supported by functional knockdown, single lab\",\n      \"pmids\": [\"23002205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Phosphorylated ATM interacts with BUB1B/BUBR1 after ionizing radiation; cells with aberrant BUB1B expression dominantly exploit mutagenic NHEJ for DNA repair in an ATM-dependent manner; FOXM1 was identified as a transcription factor causing increased BUB1B expression in CRT-recurrent bladder cancer clones.\",\n      \"method\": \"Co-immunoprecipitation of phospho-ATM with BUB1B; CRISPR/Cas9 DNA repair pathway analysis; ATM inhibitor experiments; ChIP for FOXM1\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus pharmacological inhibition and CRISPR-based pathway analysis, single lab\",\n      \"pmids\": [\"34545188\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"BubR1 (BUB1B) is a multifunctional pseudokinase/checkpoint scaffold that (1) inhibits APC/C-Cdc20 as a core component of the Mitotic Checkpoint Complex (MCC) via its KEN boxes and direct interaction with closed MAD2; (2) is activated as a kinase by direct binding to the motor CENP-E at unattached kinetochores and silenced when CENP-E captures spindle microtubules in a ternary BubR1-CENP-E-microtubule complex; (3) recruits PP2A-B56 phosphatase to kinetochores through a PLK1/CDK1-phosphorylated KARD/LxxIxE motif to counteract Aurora B and stabilize kinetochore-microtubule attachments; (4) recruits CENP-E to kinetochores via its C-terminal basic helix to facilitate chromosome alignment; (5) is regulated by post-translational modifications including PLK1 phosphorylation (promoting chromosome alignment), SIRT2-dependent deacetylation at K668 (controlling protein stability) and K250/K243 (regulating mitotic timing and meiotic fidelity), and SUMO modification at K250 (required for accurate chromosome segregation); and (6) has its transcription regulated by p53 and hStaf/ZNF143 and its abundance maintained by NAD⁺/SIRT2 signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"BUB1B (BubR1) is a dual-function mitotic regulator that both enforces the spindle assembly checkpoint (SAC) and promotes chromosome alignment, with these two activities residing in genetically separable modules [#9, #17, #21]. As a core component of the Mitotic Checkpoint Complex, BubR1 inhibits APC/C-Cdc20: its N-terminal KEN box binds Cdc20 and it directly engages closed MAD2 through MAD2 residues Arg133/Gln134, while the BubR1:Bub3 module requires phosphorylation-dependent recognition of its targets to inhibit APC/C [#9, #10, #15]. Kinetochore recruitment of BubR1/Bub3 occurs through two pools — a Bub1/Bub3-dependent pool driving alignment and a separate pool binding phosphorylated MELT repeats on KNL1 that supports robust checkpoint signaling [#16]. Beyond checkpoint control, BubR1 stabilizes kinetochore-microtubule attachments by recruiting PP2A-B56 phosphatase: PLK1/CDK1 phosphorylation of the conserved KARD/LxxIxE motif (around Ser670) creates a docking site that binds the concave groove of B56 pseudo-HEAT repeats, delivering PP2A to counteract Aurora B activity at improperly attached kinetochores [#2, #3, #4]. BubR1 also recruits CENP-E to kinetochores via its C-terminal basic helix to rescue chromosomes that fail other congression pathways, and CENP-E reciprocally controls BubR1 catalytic state — activating it at unattached kinetochores and silencing it upon microtubule capture in a ternary BubR1-CENP-E-microtubule complex [#0, #1, #22]. Although vertebrate BubR1 has degenerated into a pseudokinase whose catalysis is dispensable for error-free segregation, its ATP-binding residues remain essential for conformational stability [#5]. BubR1 abundance and activity are set by transcriptional inputs from p53 and hStaf/ZNF143 and by post-translational control, including SIRT2-dependent deacetylation that maintains protein stability and segregation fidelity [#11, #26, #27]. BubR1 haploinsufficiency causes premature sister-chromatid separation and, at deeper loss, aneuploidy [#28].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established how BubR1 catalytic state is coupled to the physical state of the kinetochore, answering how attachment status is transduced into a checkpoint signal.\",\n      \"evidence\": \"In vitro reconstitution with purified BubR1, CENP-E, and microtubules plus Xenopus egg extract depletion/add-back\",\n      \"pmids\": [\"12859900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which BubR1 substrates are phosphorylated upon activation\", \"Vertebrate pseudokinase status later complicated the kinase interpretation\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Placed BubR1 downstream of Aurora B for kinetochore localization and showed BubR1 has an alignment role beyond the checkpoint.\",\n      \"evidence\": \"Aurora B inhibitor ZM447439, RNAi, and live-cell imaging in human cells\",\n      \"pmids\": [\"12719470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking Aurora B activity to BubR1 retention under tension not defined\", \"Did not separate checkpoint from attachment contributions molecularly\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrated BubR1 stabilizes kinetochore-microtubule attachments by limiting Aurora B substrate phosphorylation, foreshadowing a phosphatase-counterbalancing role.\",\n      \"evidence\": \"siRNA depletion with Aurora inhibition rescue and CENP-A phosphorylation readout in human cells\",\n      \"pmids\": [\"15592459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the phosphatase BubR1 recruits\", \"Direct vs indirect effect on Aurora B unresolved at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved BubR1 into separable N-terminal checkpoint (GLEBS/Bub3) and C-terminal kinase-domain alignment modules.\",\n      \"evidence\": \"Domain deletion and kinase-dead mutants with mitotic timing in HeLa cells\",\n      \"pmids\": [\"15907836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Kinase-dependence of alignment later reframed by pseudokinase findings\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified p53 as a transcriptional regulator of BubR1, linking BubR1 dosage to genome stability.\",\n      \"evidence\": \"Microarray/RT-PCR and re-expression rescue in p53-null mouse cells\",\n      \"pmids\": [\"15870277\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect transcriptional control not fully established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed BubR1-containing MCC binding to APC/C requires convergent Bub1 and Aurora B kinase signals.\",\n      \"evidence\": \"Bub1 RNAi plus Aurora inhibitor with MCC-APC/C co-IP in human cells\",\n      \"pmids\": [\"16046481\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Redundancy mechanism between the two kinase arms not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linked BubR1 to the DNA damage response through a physical interaction with PARP-1.\",\n      \"evidence\": \"Affinity-MS and reciprocal co-IP with damage assays in BubR1+/- MEFs\",\n      \"pmids\": [\"16449973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of PARP-1 binding for repair not mechanistically resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placed PLK1 phosphorylation of BubR1 in the chromosome alignment pathway.\",\n      \"evidence\": \"In vitro Plk1 kinase assay, phospho-mutant rescue, and epistasis in BubR1-deficient cells\",\n      \"pmids\": [\"17376779\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector of these phospho-sites not identified at this stage\", \"Relationship to later KARD/PP2A motif not yet drawn\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified hStaf/ZNF143 and cell-cycle promoter elements driving G2/M-specific BUB1B transcription.\",\n      \"evidence\": \"Gel shift, promoter-reporter mutagenesis, and ChIP\",\n      \"pmids\": [\"17478512\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Interplay with p53 control not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided a systematic separation-of-function map distinguishing SAC (KEN/GLEBS) from attachment (proline-directed phospho-sites).\",\n      \"evidence\": \"MS phospho-site mapping, mutagenesis, co-IP, and live imaging in human cells\",\n      \"pmids\": [\"20016069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effectors of the proline-directed sites not all identified\", \"How GLEBS/Bub3 binding triggers kinetochore loading not structurally resolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the molecular basis of BubR1 engagement with closed MAD2 essential for MCC-mediated APC/C inhibition.\",\n      \"evidence\": \"Co-IP, MAD2 mutagenesis, and in vitro APC/C inhibition assays\",\n      \"pmids\": [\"21525009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How MAD2 alpha-C helix coordinates activation vs silencing not fully resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolved the phosphatase BubR1 recruits, defining the PLK1-phosphorylated KARD-PP2A-B56 axis that counters Aurora B at kinetochores.\",\n      \"evidence\": \"Domain/phospho-mutagenesis, reciprocal co-IP, Aurora B substrate and rescue assays (independently replicated)\",\n      \"pmids\": [\"23079597\", \"23345399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial regulation of PP2A delivery during attachment maturation not fully timed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Reframed vertebrate BubR1 as a pseudokinase whose catalysis is dispensable but whose ATP-binding residues stabilize conformation.\",\n      \"evidence\": \"Comparative genomics with kinase-dead complementation in human cells\",\n      \"pmids\": [\"22698286\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with earlier kinase-activity reports across species incomplete\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed CENP-E-dependent BubR1 autophosphorylation supports full checkpoint strength and alignment in human cells.\",\n      \"evidence\": \"In vitro kinase assay, phospho-mutants, CENP-E depletion, and live imaging\",\n      \"pmids\": [\"22801780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Difficult to reconcile with pseudokinase model in same year\", \"Relevant in vivo substrates not pinned down\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established NAD+/SIRT2 deacetylation at K668 as a determinant of BubR1 stability with organismal lifespan consequences.\",\n      \"evidence\": \"Acetylation-site mutagenesis, CBP identification, NMN and SIRT2-overexpression in mice with lifespan analysis\",\n      \"pmids\": [\"24825348\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How K668 acetylation triggers turnover mechanistically not fully defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided a crystal structure showing the BubR1 LxxIxE motif binds the B56 concave groove without occluding catalytic or shugoshin surfaces.\",\n      \"evidence\": \"X-ray crystallography with biochemical binding assays\",\n      \"pmids\": [\"27350047\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single lab\", \"Dynamics of phospho-dependent binding in cells not captured\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Distinguished two kinetochore BubR1/Bub3 pools with separable alignment vs checkpoint roles.\",\n      \"evidence\": \"Binding-mutant dissection, kinetochore localization, SAC assays, and co-IP\",\n      \"pmids\": [\"27457023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative partitioning between pools during mitosis not measured\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a BubR1-specific loop required for APC/C inhibition, showing BubR1:Bub3 needs phosphorylation to target APC/C distinctly from Bub1.\",\n      \"evidence\": \"In vitro APC/C inhibition and MCC assembly with mutagenesis and cellular SAC assays\",\n      \"pmids\": [\"28943088\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the phosphorylated APC/C target recognized by BubR1:Bub3 not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mapped the reciprocal BubR1 C-terminal basic helix / CENP-E acidic patch interaction required for CENP-E kinetochore recruitment and rescue congression.\",\n      \"evidence\": \"Domain mutagenesis, co-IP, localization, and alignment rescue in human cells\",\n      \"pmids\": [\"32665320\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single lab\", \"How this axis is regulated relative to PP2A recruitment not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected aberrant BUB1B expression to mutagenic NHEJ via an ATM interaction, with FOXM1 driving BUB1B upregulation in recurrent cancer.\",\n      \"evidence\": \"Phospho-ATM co-IP, CRISPR repair-pathway analysis, ATM inhibition, and FOXM1 ChIP\",\n      \"pmids\": [\"34545188\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which BubR1 biases NHEJ not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple post-translational marks (PLK1/CDK1 phosphorylation, SIRT2/CBP acetylation at K668/K250/K243, SUMO at K250) are integrated in time and space to coordinate checkpoint silencing, attachment maturation, and protein turnover remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model integrating the modifications\", \"Cross-talk between modifications and the two kinetochore pools undefined\", \"In vivo substrate(s) of residual BubR1 catalytic activity unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3, 4, 22]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 10, 15]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [6, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 16, 29]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 9, 10]}\n    ],\n    \"complexes\": [\"Mitotic Checkpoint Complex (MCC)\", \"BubR1-CENP-E-microtubule ternary complex\", \"PP2A-B56\"],\n    \"partners\": [\"CENP-E\", \"MAD2\", \"CDC20\", \"BUB3\", \"PPP2R5A\", \"PLK1\", \"PARP1\", \"ATM\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}