{"gene":"BUB1","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":1997,"finding":"Murine Bub1 localizes to the kinetochore during mitosis, and expression of a dominant-negative mutant shows Bub1 is required for both the spindle checkpoint response to spindle damage and for normal mitotic timing.","method":"Dominant-negative mutant expression, immunofluorescence localization","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — dominant-negative in mammalian cells with specific mitotic phenotype, foundational paper with 480 citations","pmids":["9182760"],"is_preprint":false},{"year":1998,"finding":"hBUB1 first appears at kinetochores during early prophase before hBUBR1; both kinases concentrate at the outer kinetochore plate and co-localize with CENP-E, suggesting they monitor kinetochore-microtubule interactions.","method":"Immunofluorescence, immunoelectron microscopy, antibody localization","journal":"Chromosoma","confidence":"High","confidence_rationale":"Tier 2 — direct localization by immunoelectron microscopy with functional context, replicated across studies","pmids":["9914370"],"is_preprint":false},{"year":1998,"finding":"Fission yeast Bub1 is recruited to centromeres upon spindle checkpoint activation and is essential for the checkpoint response to spindle damage and centromere defects; loss of bub1 causes chromosome lagging and increased chromosome loss in unperturbed mitosis.","method":"Gene deletion, immunofluorescence, live imaging","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with defined cellular phenotypes, ortholog in fission yeast","pmids":["9864354"],"is_preprint":false},{"year":1999,"finding":"BUB1 and BUB3 form a complex of monomers that interacts with MAD1; this multiprotein complex exhibits kinase activity requiring Lys821 in the BUB1 kinase motif, resulting in BUB1 autophosphorylation and phosphorylation of associated MAD1.","method":"In vitro kinase assay, co-immunoprecipitation, site-directed mutagenesis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1/2 — in vitro kinase assay with mutagenesis, single study","pmids":["10198256"],"is_preprint":false},{"year":2001,"finding":"Bub1 localizes to kinetochores during meiosis I and II in Xenopus oocytes; its electrophoretic mobility shifts (reflecting phosphorylation and activation) during meiosis I, and this activation is MAPK-dependent and can be induced by p90(Rsk), which phosphorylates Bub1 in vitro and increases its kinase activity.","method":"In vitro kinase assay, immunofluorescence, MEK inhibitor (U0126), injection of constitutively active p90Rsk","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation plus in vivo reconstitution with multiple orthogonal approaches","pmids":["11231148"],"is_preprint":false},{"year":2001,"finding":"In mammalian cells, Bub1 and BubR1 are recruited to kinetochores in response to loss of tension (low-dose vinblastine) but not microtubule detachment, while Mad2 responds to attachment loss; Mad2 does not associate with Bub1 or BubR1, indicating they operate in distinct checkpoint pathways.","method":"Immunofluorescence with microtubule toxins at defined doses, co-immunoprecipitation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods distinguishing tension vs. attachment pathways","pmids":["11274370"],"is_preprint":false},{"year":2001,"finding":"Bub1 and BubR1 are part of a common complex during mitosis; Bub1 localization is sensitive to both tension and microtubule attachment (asymmetric at kinetochores, dependent on microtubule attachment), while BubR1 localization is symmetrical; Bub1 is rapidly phosphorylated by nocodazole or taxol treatment.","method":"Immunofluorescence, cell synchronization, microtubule toxin treatment","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — systematic localization studies with functional context, single lab","pmids":["11792804"],"is_preprint":false},{"year":2001,"finding":"Fission yeast Bub1 is essential for the meiotic pattern of chromosome segregation: Bub1 deletion causes sister kinetochores to disunite at MI and prevents retention of Rec8 cohesin at centromeres at anaphase I, revealing roles in sister kinetochore co-orientation and centromeric cohesion beyond spindle checkpoint.","method":"Gene deletion, live imaging, immunofluorescence","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with multiple defined meiotic phenotypes, ortholog","pmids":["11331883"],"is_preprint":false},{"year":2002,"finding":"Immunodepletion of Bub1 from Xenopus egg extracts blocks Mos-dependent establishment of CSF arrest; rescue requires wild-type but not kinase-dead Bub1, demonstrating that Bub1 kinase activity is required for establishment of meiotic metaphase arrest and APC inhibition downstream of MAPK/Rsk.","method":"Immunodepletion from egg extracts, kinase-dead rescue, in vitro reconstitution","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in egg extracts with kinase-dead mutant rescue","pmids":["12123578"],"is_preprint":false},{"year":2004,"finding":"Bub1 directly phosphorylates Cdc20 in vitro and catalytically inhibits APC/C(Cdc20) ubiquitin ligase activity; a Cdc20 mutant with all six Bub1 phosphorylation sites removed is refractory to inhibition; upon checkpoint activation, Bub1 kinase activity toward Cdc20 is stimulated; expression of non-phosphorylatable Cdc20 allows mitotic exit despite spindle damage.","method":"In vitro kinase assay, site-directed mutagenesis, APC/C ubiquitination assay, RNAi in HeLa cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis plus cellular rescue, multiple orthogonal methods","pmids":["15525512"],"is_preprint":false},{"year":2004,"finding":"Xenopus Bub1 is hyperphosphorylated and activated on unattached chromosomes; MAPK phosphorylates Bub1 at consensus sites and is required for this activation; activated Bub1 enhances checkpoint efficiency and promotes recruitment of other checkpoint proteins to kinetochores.","method":"In vitro kinase assay, MAPK inhibition, site-directed mutagenesis, checkpoint assay in Xenopus","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with mutagenesis and cellular validation","pmids":["15241477"],"is_preprint":false},{"year":2005,"finding":"Human Bub1 is required for centromeric localization of Sgo1 (shugoshin) during mitosis; Bub1 depletion causes Sgo1 to redistribute along chromosome arms and leads to loosening of centromeric cohesion.","method":"RNAi knockdown, immunofluorescence, live-cell imaging","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — RNAi with specific localization and functional cohesion phenotype, replicated in subsequent studies","pmids":["15723797"],"is_preprint":false},{"year":2005,"finding":"Bub1 depletion leads to accumulation of misaligned chromatids with both sister kinetochores linked to microtubules abnormally; Bub1 and Aurora B are recruited to kinetochores independently of each other and have additive effects when co-depleted, indicating parallel pathways for stable bipolar kinetochore-microtubule attachment.","method":"RNAi, live-cell imaging, fluorescence microscopy, double-depletion epistasis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis by double depletion with defined cellular phenotype","pmids":["15933723"],"is_preprint":false},{"year":2006,"finding":"Plk1 binds Bub1 through its polo-box domain (PBD) in mitotic cells; this interaction requires Cdk1-mediated phosphorylation of Bub1 at T609; Bub1 depletion diminishes kinetochore localization of Plk1, and expression of wild-type but not T609A Bub1 restores Plk1 kinetochore localization.","method":"Co-immunoprecipitation, site-directed mutagenesis, RNAi, immunofluorescence, in vitro kinase assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal pulldown with mutagenesis and cellular rescue experiment","pmids":["16760428"],"is_preprint":false},{"year":2006,"finding":"Bub1 is degraded during mitotic exit by APC/C(Cdh1) through two KEN-box motifs; mutation of both KEN boxes stabilizes Bub1 in cells; Bub1 is ubiquitinated by immunopurified APC/C(Cdh1) in vitro.","method":"In vitro ubiquitination assay, site-directed mutagenesis, RNAi of Cdh1, protein stability assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro ubiquitination reconstitution plus mutagenesis and cellular validation","pmids":["17158872"],"is_preprint":false},{"year":2007,"finding":"Budding yeast Bub1 kinase domain is required for accurate chromosome biorientation after nocodazole release; Bub1 kinase mislocalizes Sgo1p when absent, and both kinase domain and Sgo1 are required for efficient biorientation.","method":"Kinase-domain deletion, live imaging, immunofluorescence, genetic epistasis","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with epistasis and defined phenotype, ortholog","pmids":["18081426"],"is_preprint":false},{"year":2007,"finding":"In fission yeast, Bub1 acts as a stable kinetochore scaffold (confirmed by FRAP); tethering Bub1 to telomeres is sufficient to recruit anaphase inhibitors (Mad2, Mad3) in a kinase-independent manner.","method":"FRAP, ectopic tethering to telomeres, kinetochore recruitment assay","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — FRAP plus gain-of-function tethering with functional readout, ortholog","pmids":["18094750"],"is_preprint":false},{"year":2007,"finding":"BUB1 depletion in normal human fibroblasts via RNAi triggers premature senescence dependent on p53 and its target p21(CIP1); cells with reduced Bub1 and inactivated p53 become highly aneuploid, revealing a surveillance mechanism linking Bub1 loss to the p53 pathway.","method":"RNAi knockdown, dominant-negative p53, p21 depletion, senescence assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — epistasis via double knockdown/dominant-negative with specific phenotypic readout","pmids":["17488820"],"is_preprint":false},{"year":2008,"finding":"Crystal structure of the Bub1 kinase domain reveals an N-terminal extension required for kinase activity; the activation segment has active-kinase features but its C-terminal portion sterically restricts substrate access; Bub1 uses KEN-box docking motifs outside the kinase domain to recruit Cdc20, and these KEN boxes are required for spindle checkpoint function in human cells.","method":"X-ray crystallography, mutagenesis, in vitro kinase assay, checkpoint assay in HeLa cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation by mutagenesis and cellular assay","pmids":["18995837"],"is_preprint":false},{"year":2008,"finding":"SV40 large T antigen binds Bub1 directly; T antigen coimmunoprecipitates with endogenous Bub1 and Bub3; spindle checkpoint override by T antigen depends on Bub1 binding, and T antigen-induced tetraploidy and DNA damage response (p53 stabilization via ATM/ATR) are also Bub1-binding dependent.","method":"Co-immunoprecipitation, genetic analysis (T antigen mutants), DNA damage markers","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2/3 — Co-IP with multiple phenotypic readouts, single lab","pmids":["18922873"],"is_preprint":false},{"year":2009,"finding":"Bub1 phosphorylates the conserved serine 121 of histone H2A in fission yeast; this phosphorylation is required for centromeric localization of shugoshin proteins; h2a-SA mutant phenocopies bub1 kinase-dead mutant; artificial tethering of shugoshin to centromeres rescues CIN defects in both h2a-SA and bub1-KD mutants.","method":"In vitro kinase assay, site-directed mutagenesis, ectopic tethering rescue, genetic epistasis","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis, epistasis, and functional rescue, replicated across labs","pmids":["19965387"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the N-terminal TPR region of BUB1 at 1.74 Å resolution; functional mutagenesis identifies residues important for interaction with the kinetochore protein Blinkin (KNL1), which is required for kinetochore localization and function of BUB1 in the SAC.","method":"X-ray crystallography, site-directed mutagenesis, in vivo localization assay","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional mutagenesis validation","pmids":["19141287"],"is_preprint":false},{"year":2009,"finding":"In oocytes, Bub1 controls APC/C activation timing: Bub1 deletion accelerates APC/C-mediated securin destruction by ~5 hours; Bub1's kinase domain is not required for this APC/C delay; premature chiasmata resolution in Bub1-deficient oocytes requires APC/C and separase activity.","method":"Cre-lox conditional oocyte knockout, quantitative APC/C activity assay, genetic epistasis with Apc2 and separase","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — conditional knockout with quantitative biochemical readout and genetic epistasis","pmids":["19249208"],"is_preprint":false},{"year":2010,"finding":"Sgo1 is first recruited to centromeric heterochromatin in G2 in an HP1-dependent but Bub1-kinase-independent manner; during prophase, Sgo1 centromeric re-localization requires Bub1 kinase activity; Bub1 kinase activity is not required for checkpoint function or chromosome alignment in mammalian cells using BUB1-null MEF complementation.","method":"Null MEF complementation with kinase-dead Bub1, live-cell imaging, immunofluorescence across cell cycle stages","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — null MEF complementation with kinase-dead Bub1, multiple orthogonal observations","pmids":["20124418"],"is_preprint":false},{"year":2011,"finding":"Bub1 overexpression in mice causes aberrant kinase activity and hyperactivation of Aurora B kinase, leading to chromosome misalignment/lagging and aneuploidy; pharmacological or genetic (BubR1 overexpression) suppression of Aurora B corrects these errors, placing Aurora B downstream of Bub1 overexpression.","method":"Transgenic mouse overexpression, Aurora B inhibition, epistasis by BubR1 overexpression, live imaging","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — in vivo transgenic model with pharmacological and genetic epistasis","pmids":["21646403"],"is_preprint":false},{"year":2012,"finding":"Mps1 is the major kinase copurifying with yeast kinetochore particles and phosphorylates conserved MELT motifs in Spc105/KNL1; this phosphorylation recruits Bub1 to kinetochores and is reversed by PP1; Spc105 mutants lacking MELT phosphorylation sites are checkpoint-defective.","method":"Kinetochore particle purification, in vitro kinase assay, phosphosite mutagenesis, checkpoint assay","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis and checkpoint functional readout, replicated by parallel study","pmids":["22521787"],"is_preprint":false},{"year":2012,"finding":"Mps1 (Mph1) phosphorylation of MELT motifs in Spc7 (KNL1 ortholog) recruits Bub1 and Bub3 to kinetochores in fission yeast, and this recruitment is required to maintain SAC signaling.","method":"Phosphosite mutagenesis, kinetochore recruitment assay, checkpoint assay","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — genetic mutagenesis with functional checkpoint readout, replicated by parallel study","pmids":["22521786"],"is_preprint":false},{"year":2012,"finding":"Crystal structure of Bub1 TPR domain in complex with KNL1 KI motif; interaction occurs along the convex TPR surface; point mutations on this surface impair Bub1-KNL1 interaction in vitro and in vivo; a 62-residue segment C-terminal to the TPRs including the Bub3-binding domain is necessary and largely sufficient for kinetochore recruitment.","method":"X-ray crystallography, site-directed mutagenesis, in vitro binding, in vivo kinetochore localization assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis with in vivo validation","pmids":["22331848"],"is_preprint":false},{"year":2012,"finding":"Bub1 kinase activity drives error correction and mitotic checkpoint signaling in mice via phosphorylation of histone H2A at T121, which controls Aurora B kinase localization and activity; mice lacking Bub1 kinase activity show substantial chromosome segregation errors but no increased tumor susceptibility.","method":"Knockin mouse (kinase-dead), H2A-T121 phosphorylation assay, Aurora B localization, tumor analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — knockin mouse model with multiple defined molecular and cellular readouts","pmids":["23209306"],"is_preprint":false},{"year":2014,"finding":"Mad1 kinetochore localization in budding yeast is mediated by Mps1 phosphorylation of a conserved region within Bub1; tethering this Bub1 region to kinetochores bypasses the need for upstream checkpoint recruitment of Mps1; the Mad1 interaction with Bub1 and kinetochores can be reconstituted with Mps1 and Mad2 in vitro.","method":"Reconstitution in vitro, kinetochore tethering bypass, checkpoint genetics","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus bypass tethering experiment","pmids":["24402315"],"is_preprint":false},{"year":2014,"finding":"Phosphorylation at the P+1 loop of human Bub1 enhances its activity specifically toward H2A but not Cdc20; crystal structure of phosphorylated Bub1 reveals phosphorylation-triggered reorganization of the P+1 loop; this activating phosphorylation occurs constitutively during the cell cycle and appears to be intramolecular autophosphorylation; enrichment of H2A-pT120 at mitotic kinetochores requires kinetochore targeting of Bub1.","method":"X-ray crystallography, in vitro kinase assay, substrate-specific phosphorylation, mutagenesis","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus in vitro kinase assay with mutagenesis","pmids":["25308863"],"is_preprint":false},{"year":2014,"finding":"BuGZ binds and stabilizes Bub3 during interphase and mitosis through its GLEBS domain; BuGZ inhibition causes loss of both Bub3 and Bub1 from kinetochores, reduction of Bub1-dependent H2A phosphorylation at centromeres, and attenuation of Aurora B activity, leading to chromosome congression defects.","method":"RNAi, co-immunoprecipitation, immunofluorescence, phosphorylation assay","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — Co-IP plus functional cascade with multiple readouts, single lab","pmids":["24462187"],"is_preprint":false},{"year":2015,"finding":"Bub1 and BubR1 heterodimerize with each other at a pseudo-symmetric interface; Bub1 (but not BubR1) enhances Bub3 binding to phosphorylated kinetochores; grafting a short Bub1 motif onto BubR1 promotes Bub1-independent kinetochore recruitment of BubR1 but cannot sustain a functional checkpoint; kinetochore localization of BubR1 requires direct heterodimerization with Bub1.","method":"Structural analysis, in vitro binding, mutagenesis, gain-of-function chimera, checkpoint assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1/2 — structure plus multiple functional assays demonstrating mechanism of sub-functionalization","pmids":["25611342"],"is_preprint":false},{"year":2015,"finding":"Bub1 kinase activity promotes TGF-β signaling: Bub1 interacts with TGFBRI and TGFBRII forming a ternary complex, promotes receptor heterodimerization, and is required for SMAD3 recruitment, SMAD2/3 phosphorylation, and SMAD-dependent transcription; a kinase-dead Bub1 mutant and small-molecule inhibitor (2OH-BNPP1) suppress TGF-β signaling.","method":"RNAi kinome screen, co-immunoprecipitation, kinase-dead mutant, small-molecule inhibitor, in vivo xenograft","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, kinase-dead, inhibitor, in vivo) showing mechanistic pathway role","pmids":["25564677"],"is_preprint":false},{"year":2015,"finding":"Human BUB1 contributes to SAC signaling through a 50-amino-acid segment containing an ABBA motif and KEN box that promotes efficient CDC20 binding at kinetochores; kinetochore recruitment of BUBR1 and BUB3 by BUB1 is dispensable for SAC activation; human BUB1 does not stably associate with MAD1.","method":"Domain deletion/mutagenesis, complementation, checkpoint assay, Co-IP","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — domain mutagenesis with rescue and checkpoint functional readout","pmids":["26148513"],"is_preprint":false},{"year":2015,"finding":"Distinct domains within Bub1 mediate kinetochore recruitment of RZZ complex and BubR1 separately; the middle region of Bub1 contributes to RZZ localization; a distinct region mediates BubR1 kinetochore localization through direct binding; removal of the BubR1-recruiting region paradoxically increases checkpoint strength.","method":"Domain deletion, Co-IP, immunofluorescence, checkpoint assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with functional checkpoint phenotype, multiple orthogonal methods","pmids":["26031201"],"is_preprint":false},{"year":2015,"finding":"Bub1 autophosphorylation at T589 controls kinetochore turnover of Bub1; T589A mutation causes uniform H2A-T120 phosphorylation along chromosome arms and aberrant Sgo1 recruitment; kinetochore tethering of Bub1-T589A refocuses H2A-T120 phosphorylation to centromeres, linking Bub1 kinetochore docking to localized H2A phosphorylation.","method":"Quantitative phosphoproteomics, autophosphorylation assay, site-directed mutagenesis, kinetochore tethering","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1/2 — phosphoproteomics plus mutagenesis and tethering rescue","pmids":["26399325"],"is_preprint":false},{"year":2016,"finding":"Bub1 inhibition (BAY-320 and BAY-524) reduces shugoshin and chromosomal passenger complex (CPC/Aurora B) chromosomal association, impairs chromosome arm resolution, and sensitizes cells to paclitaxel; Bub1 inhibition has only minor effects on mitotic progression or SAC function, distinguishing scaffolding from catalytic roles.","method":"Small-molecule kinase inhibitors (BAY-320, BAY-524), immunofluorescence, mitotic timing assay, drug combination assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1/2 — potent selective inhibitors with multiple readouts comparing inhibition vs. depletion phenotypes","pmids":["26885717"],"is_preprint":false},{"year":2016,"finding":"Bub1 scaffolds Plk1-mediated phosphorylation of Cdc20; Bub1-Plk1-dependent Cdc20 phosphorylation inhibits APC/C(Cdc20) in vitro, is required for checkpoint signaling in human cells, and acts in a parallel pathway to MCC formation; a phospho-mimicking Cdc20 mutant restores mitotic arrest in Mad2 or BubR1-depleted cells.","method":"In vitro APC/C assay, Co-IP, RNAi, phospho-mimetic rescue, checkpoint assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro APC/C assay with mutagenesis and genetic epistasis","pmids":["26912231"],"is_preprint":false},{"year":2016,"finding":"In fission yeast, multisite binding of Bub3 to the Spc7 MELT array toggles the spindle checkpoint switch by permitting Mph1 (Mps1)-dependent interaction of Bub1 with Mad1-Mad2.","method":"Phosphosite mutagenesis, checkpoint functional assay, Co-IP","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 — genetic/biochemical mechanism in yeast ortholog, single study","pmids":["27618268"],"is_preprint":false},{"year":2017,"finding":"In fission yeast meiosis, Moa1 (meikin) recruits Plo1 (polo-like kinase) to kinetochores to phosphorylate Spc7 (KNL1) and accumulate Bub1, causing meiotic Bub1 to persist at kinetochores until anaphase I; this ensures robust Sgo1 localization and centromeric cohesion protection; this meiosis-specific Bub1 regulation is conserved in mouse.","method":"Genetic analysis, immunofluorescence, kinase assay, mouse meiosis analysis","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with mechanistic biochemical evidence, ortholog","pmids":["28497540"],"is_preprint":false},{"year":2018,"finding":"The BUB3-BUB1 complex binds to telomeres during S phase and promotes telomere DNA replication; loss of the complex causes fragile and shortened telomeres; TRF2 targets BUB1-BUB3 to telomeres; BUB1 directly phosphorylates TRF1 to promote recruitment of BLM helicase for resolution of replication stress.","method":"Co-immunoprecipitation, in vitro kinase assay, chromatin fractionation, telomere replication assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay with Co-IP and functional telomere replication readout","pmids":["29727616"],"is_preprint":false},{"year":2018,"finding":"Malonylation of histone H2A at K119 inhibits the interaction between Bub1 and H2A, reducing Bub1-dependent H2A-S121 phosphorylation in vitro and causing loss of shugoshin chromosomal localization; anionic mutations at K119 phenocopy this in yeast.","method":"In vitro peptide binding assay, in vitro kinase assay, site-directed mutagenesis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro biochemical assay with mutagenesis, single study","pmids":["29769606"],"is_preprint":false},{"year":2018,"finding":"In human cells, RZZ's sole role in SAC activation is to tether Mad1-Mad2 to kinetochores; Bub1 and KNL1 activate kinetochore-bound Mad1-Mad2 to produce a 'wait anaphase' signal but are not required for fibrous corona formation; Mps1 phosphorylates Rod to trigger corona formation independently of Bub1.","method":"Genome editing (BUB1 disruption), RNAi, checkpoint assay, immunofluorescence","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — complete genetic removal via genome editing with multiple functional readouts","pmids":["30415700"],"is_preprint":false},{"year":2019,"finding":"Efficient spindle checkpoint signaling requires integrated activities of Bub1 and the RZZ complex; Rod removal reduces proximity of Bub1 and Mad1; bypassing Rod requirement by tethering Mad1 or strengthening Bub1-Mad1 interaction is sufficient; Bub1 has checkpoint functions independent of Mad1 localization, suggesting a catalytic role.","method":"Genome editing + RNAi, proximity ligation assay, tethering bypass, checkpoint assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — genome editing with tethering bypass and multiple functional readouts","pmids":["30782962"],"is_preprint":false},{"year":2020,"finding":"Either Haspin or Bub1 activity is sufficient to recruit Aurora B to distinct chromosomal loci; joint inhibition of both kinases fully abolishes Aurora B accumulation at centromeres, impairing correction of erroneous KT-MT attachments; Aurora B substrates at the kinetochore (Hec1, Dsn1, Knl1) are phosphorylated independently of centromere-localized Aurora B pools.","method":"Kinase inhibition (single and combined), immunofluorescence, chromosome segregation assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — double kinase inhibition epistasis with multiple molecular readouts","pmids":["32027339"],"is_preprint":false},{"year":2021,"finding":"Aurora B kinase directly promotes MCC production by working downstream of Mps1 in budding yeast and human cells; conditional dimerization of Aurora B with Bub1 (but not with the Spc105 phosphodomain) leads to ectopic MCC production; Bub1 must recruit both Mad1 and Cdc20 for this signaling; Aurora B cooperates with Bub1 after Mps1 licenses Bub1 recruitment.","method":"Ectopic SAC activation (eSAC) system, conditional dimerization, checkpoint assay in yeast and HeLa cells","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — gain-of-function tethering system with epistasis in two organisms","pmids":["34861183"],"is_preprint":false},{"year":2021,"finding":"BUB1 directly interacts with STAT3 and mediates phosphorylation of STAT3 at Ser727; pharmacological inhibition of BUB1 kinase activity or BUB1 kinase-domain mutation abrogates STAT3 transcriptional activation; BUB1 kinase inhibition suppresses bladder cancer cell growth in vitro and in vivo.","method":"Co-immunoprecipitation, in vitro kinase assay, kinase-dead mutant, pharmacological inhibitor, xenograft","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with kinase-dead mutant and inhibitor, single lab","pmids":["34852826"],"is_preprint":false},{"year":2021,"finding":"Crystal structure of Mad1 C-terminal domain bound to two phosphorylated Bub1 CD1 peptides at 1.75 Å; phosphorylated Bub1 Thr461 interacts with Arg617 of the Mad1 RLK motif and acts as N-terminal cap to the CD1 α-helix dipole; only one Bub1 CD1 peptide binds the Mad1 homodimer in solution due to inherent asymmetry in the Mad1 coiled-coil.","method":"X-ray crystallography, NMR, solution binding assay","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with solution binding validation","pmids":["34013668"],"is_preprint":false},{"year":2022,"finding":"Mps1 phosphorylation of both Bub1 CD1 and Mad1 CTD generates a tripartite assembly of Bub1 and Cdc20 on Mad1 CTD; this positions Cdc20's Mad2-interacting motif (MIM) near open-Mad2 to catalyze C-Mad2:Cdc20 formation and MCC assembly.","method":"X-ray crystallography, cross-linking mass spectrometry, in vitro reconstitution of MCC assembly","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — structural and biochemical reconstitution with multiple orthogonal methods","pmids":["36289199"],"is_preprint":false}],"current_model":"BUB1 is a multifunctional serine/threonine kinase that (1) localizes to kinetochores via its N-terminal TPR domain binding to phospho-MELT motifs of KNL1/Spc105 (phosphorylated by Mps1/Mph1), where it acts as a scaffold recruiting BubR1, BUB3, RZZ, and Mad1-Mad2 for spindle assembly checkpoint (SAC) signaling; (2) directly phosphorylates histone H2A at T120/S121 to recruit shugoshin proteins and thereby protect centromeric cohesion; (3) phosphorylates and inhibits the APC/C activator Cdc20 (both directly and by scaffolding Plk1), and is itself degraded by APC/C(Cdh1) via KEN-box motifs; (4) recruits Plk1 to kinetochores via a Cdk1-phospho-T609 docking site; (5) cooperates with Aurora B and Haspin to generate the inner centromere Aurora B pool that corrects erroneous kinetochore-microtubule attachments; and (6) has roles beyond mitosis including promotion of TGF-β receptor signaling, telomere replication via TRF2-dependent recruitment and TRF1 phosphorylation, and DNA damage response activation through ATM-mediated phosphorylation."},"narrative":{"teleology":[{"year":1997,"claim":"Establishing BUB1 as a kinetochore-localized kinase required for the spindle assembly checkpoint answered the foundational question of whether vertebrate cells use checkpoint kinases analogous to yeast Bub1.","evidence":"Dominant-negative mutant expression and immunofluorescence in mammalian cells","pmids":["9182760"],"confidence":"High","gaps":["Endogenous substrates unknown","Mechanism of kinetochore recruitment undefined","Relationship to BubR1 not established"]},{"year":1998,"claim":"Localization studies resolved when and where BUB1 acts: it arrives at outer kinetochores in early prophase before BubR1, and in fission yeast is essential for both checkpoint response and accurate chromosome segregation in unperturbed mitosis.","evidence":"Immunoelectron microscopy in human cells; gene deletion in fission yeast with live imaging","pmids":["9914370","9864354"],"confidence":"High","gaps":["Mechanism of kinetochore targeting still unknown","No structural information on BUB1 domains"]},{"year":2001,"claim":"Multiple studies established that BUB1 has functions beyond checkpoint signaling: it is required for meiotic sister kinetochore co-orientation and centromeric cohesion protection in fission yeast, and is activated by the MAPK/p90Rsk pathway during meiosis.","evidence":"Gene deletion in fission yeast meiosis; kinase assays and MEK inhibition in Xenopus oocytes","pmids":["11331883","11231148","11274370"],"confidence":"High","gaps":["Substrate linking BUB1 to cohesion protection not identified","Mechanism of MAPK-mediated activation unclear structurally"]},{"year":2004,"claim":"Identification of Cdc20 as a direct BUB1 kinase substrate explained how BUB1 catalytic activity inhibits APC/C: phosphorylation of six Cdc20 sites blocks APC/C activation, and non-phosphorylatable Cdc20 permits mitotic exit despite spindle damage.","evidence":"In vitro kinase and APC/C ubiquitination assays with site-directed mutagenesis; RNAi in HeLa cells","pmids":["15525512"],"confidence":"High","gaps":["Whether Cdc20 phosphorylation is sufficient for checkpoint in vivo uncertain","Other catalytic substrates not yet identified"]},{"year":2005,"claim":"Discovery that BUB1 is required for centromeric localization of shugoshin (Sgo1) and for accurate bipolar kinetochore–microtubule attachment linked BUB1 to cohesion protection and error correction pathways distinct from its checkpoint role.","evidence":"RNAi in human cells with localization and cohesion phenotypes; epistasis with Aurora B","pmids":["15723797","15933723"],"confidence":"High","gaps":["Direct BUB1 substrate mediating Sgo1 recruitment unknown","Mechanism of parallel action with Aurora B not resolved"]},{"year":2006,"claim":"BUB1 was shown to recruit Plk1 to kinetochores via Cdk1-phosphorylated T609, and to be degraded by APC/C(Cdh1) through KEN-box motifs, establishing BUB1 as both a scaffold for Plk1 and a regulated APC/C substrate.","evidence":"Reciprocal Co-IP with T609A mutagenesis; in vitro ubiquitination by APC/C(Cdh1) with KEN-box mutagenesis","pmids":["16760428","17158872"],"confidence":"High","gaps":["Functional consequence of Plk1 recruitment via BUB1 not yet defined","How KEN boxes coordinate Cdc20 binding vs. APC/C-mediated degradation unclear"]},{"year":2008,"claim":"Crystal structure of the BUB1 kinase domain revealed an N-terminal extension required for activity and showed that BUB1 uses KEN-box motifs to dock Cdc20 for checkpoint signaling, resolving how a single kinase accomplishes both catalytic and scaffolding functions.","evidence":"X-ray crystallography with mutagenesis and checkpoint assay in HeLa cells","pmids":["18995837"],"confidence":"High","gaps":["Substrate selectivity mechanism not resolved","How kinase domain activation segment restricts access unknown"]},{"year":2009,"claim":"Identification of histone H2A S121 (T120 in mammals) as the direct BUB1 kinase substrate responsible for shugoshin recruitment answered a long-standing question about the molecular mechanism connecting BUB1 kinase activity to cohesion protection.","evidence":"In vitro kinase assay, h2a-SA mutagenesis phenocopying bub1-KD, ectopic tethering rescue in fission yeast","pmids":["19965387"],"confidence":"High","gaps":["Structural basis of H2A recognition by BUB1 unknown","Whether this mechanism is fully conserved in mammals not yet confirmed"]},{"year":2009,"claim":"The crystal structure of BUB1's TPR domain and its interaction with KNL1 defined the structural basis of BUB1 kinetochore recruitment, answering how BUB1 docks at unattached kinetochores.","evidence":"X-ray crystallography at 1.74 Å with functional mutagenesis and localization assay","pmids":["19141287"],"confidence":"High","gaps":["How phospho-MELT recognition integrates with TPR–KI interaction not yet clear"]},{"year":2012,"claim":"Parallel studies in budding and fission yeast established that Mps1 phosphorylation of MELT motifs on KNL1/Spc105 is the signal that recruits BUB1–BUB3, explaining the upstream regulation of BUB1 kinetochore targeting and linking it to unattached kinetochore status.","evidence":"Kinetochore particle purification, in vitro kinase assay, phosphosite mutagenesis in S. cerevisiae and S. pombe","pmids":["22521787","22521786"],"confidence":"High","gaps":["Valency and cooperativity of multi-MELT engagement not yet quantified","PP1 reversal kinetics not defined"]},{"year":2012,"claim":"A kinase-dead knockin mouse demonstrated that BUB1 kinase activity drives H2A-T121 phosphorylation, Aurora B centromeric localization, and error correction in vivo, but is dispensable for tumor suppression, separating catalytic from scaffolding functions in a mammalian organism.","evidence":"Knockin mouse model with H2A-T121 phosphorylation and Aurora B localization assays","pmids":["23209306"],"confidence":"High","gaps":["Why kinase-dead mice lack tumor susceptibility despite segregation errors is unexplained","Contribution of scaffolding vs. kinase to SAC not fully delineated in vivo"]},{"year":2015,"claim":"Domain mapping in human BUB1 resolved how a single scaffold protein recruits distinct checkpoint effectors: separate domains mediate BubR1 heterodimerization, RZZ recruitment, and Cdc20 binding (via ABBA motif and KEN box), while BUB1 enhances BUB3 phospho-MELT binding to explain why BubR1 depends on BUB1 for kinetochore access.","evidence":"Structural analysis, domain deletion, chimeric constructs, checkpoint and localization assays","pmids":["25611342","26031201","26148513"],"confidence":"High","gaps":["How removal of BubR1-recruiting domain increases checkpoint strength is paradoxical and unexplained","Stoichiometry of BUB1 scaffold complexes at kinetochores undefined"]},{"year":2015,"claim":"Discovery that BUB1 promotes TGF-β signaling by forming a ternary complex with TGF-β receptors and facilitating SMAD phosphorylation established a non-mitotic function for BUB1 kinase activity in a major signaling pathway.","evidence":"RNAi kinome screen, Co-IP, kinase-dead mutant, small-molecule inhibitor, xenograft model","pmids":["25564677"],"confidence":"High","gaps":["Direct BUB1 phosphorylation target in TGF-β pathway not identified","How cytoplasmic TGF-β signaling interfaces with kinetochore BUB1 pool unclear"]},{"year":2016,"claim":"Selective BUB1 kinase inhibitors (BAY-320/BAY-524) confirmed that catalytic activity is specifically required for shugoshin and Aurora B chromosomal localization but has only minor effects on SAC function, definitively separating kinase-dependent from scaffold-dependent roles.","evidence":"Small-molecule kinase inhibitors with immunofluorescence, mitotic timing, and drug combination assays","pmids":["26885717"],"confidence":"High","gaps":["Whether kinase inhibition sensitizes tumors to taxanes in patients untested","Off-target effects not fully excluded"]},{"year":2016,"claim":"BUB1 was shown to scaffold Plk1-mediated phosphorylation of Cdc20 as a parallel APC/C inhibitory mechanism alongside MCC formation, resolving the functional consequence of the BUB1-Plk1 interaction discovered a decade earlier.","evidence":"In vitro APC/C assay, RNAi, phospho-mimetic Cdc20 rescue of Mad2/BubR1-depleted cells","pmids":["26912231"],"confidence":"High","gaps":["Relative contribution of direct BUB1 vs. BUB1-scaffolded Plk1 phosphorylation of Cdc20 not quantified in vivo"]},{"year":2018,"claim":"BUB1–BUB3 was found to localize to telomeres during S phase via TRF2 and phosphorylate TRF1 to recruit BLM helicase for replication stress resolution, establishing a replication function entirely outside mitosis.","evidence":"Co-IP, in vitro kinase assay, chromatin fractionation, telomere replication assay","pmids":["29727616"],"confidence":"High","gaps":["BUB1 phosphosite(s) on TRF1 not mapped","Whether telomere shortening phenotype is kinase-dependent not fully tested"]},{"year":2020,"claim":"Combined inhibition of BUB1 and Haspin fully abolished centromeric Aurora B accumulation, demonstrating that two parallel histone-mark pathways converge to position the chromosomal passenger complex for error correction.","evidence":"Single and combined kinase inhibition with immunofluorescence and segregation assays","pmids":["32027339"],"confidence":"High","gaps":["Whether Aurora B at other loci compensates for centromeric loss not fully resolved","Quantitative contribution of each pathway varies by cell type"]},{"year":2022,"claim":"Structural reconstitution of the Mps1-phosphorylated Bub1–Cdc20–Mad1 CTD tripartite complex explained the catalytic mechanism of MCC assembly: Bub1 and Cdc20 are co-positioned on Mad1 to present Cdc20's Mad2-interacting motif near open-Mad2, resolving the long-sought template model for checkpoint signal generation.","evidence":"X-ray crystallography, cross-linking mass spectrometry, in vitro MCC reconstitution","pmids":["36289199"],"confidence":"High","gaps":["How kinetochore geometry and valency modulate catalytic rate not determined","Full-length reconstitution of the signaling cascade from Mps1 through MCC not achieved"]},{"year":null,"claim":"Key unresolved questions include: how BUB1's mitotic and interphase pools are differentially regulated, the structural basis for substrate selectivity between H2A and Cdc20, quantitative contributions of BUB1's scaffold versus kinase activities to SAC robustness in human tissues, and whether BUB1 kinase inhibition has therapeutic utility.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length BUB1 structure","No in vivo quantitative model integrating all BUB1 activities","Therapeutic window for BUB1 kinase inhibition not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,9,20,30,33,41,47]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[16,32,35,38]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[20,30,42]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,1,2,25,27,28]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[41]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2,9,25,28,37,49]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[33]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[41]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[20,30,42]}],"complexes":["BUB1–BUB3","MCC (mitotic checkpoint complex)"],"partners":["BUB3","BUBR1","MAD1","CDC20","KNL1","PLK1","SGO1","TRF2"],"other_free_text":[]},"mechanistic_narrative":"BUB1 is a conserved serine/threonine kinase that functions as a central kinetochore scaffold and catalytic hub coordinating spindle assembly checkpoint (SAC) signaling, chromosome biorientation, and centromeric cohesion protection during cell division. BUB1 is recruited to kinetochores via its N-terminal TPR domain binding Mps1-phosphorylated MELT motifs on KNL1/Spc105, where it scaffolds recruitment of BubR1, RZZ, and Mad1–Mad2 through distinct domains, and positions Cdc20 on Mad1 to catalyze mitotic checkpoint complex (MCC) assembly [PMID:25611342, PMID:36289199, PMID:22521787]. Its kinase activity phosphorylates histone H2A at T120/S121 to recruit shugoshin proteins for centromeric cohesion protection and to localize Aurora B for error correction of kinetochore–microtubule attachments, while it also directly and indirectly (via Plk1 scaffolding) phosphorylates Cdc20 to inhibit APC/C [PMID:19965387, PMID:15525512, PMID:26912231, PMID:23209306]. Beyond mitosis, BUB1 promotes TGF-β receptor signaling by facilitating receptor heterodimerization and SMAD phosphorylation, and supports telomere replication by phosphorylating TRF1 downstream of TRF2-dependent recruitment [PMID:25564677, PMID:29727616]."},"prefetch_data":{"uniprot":{"accession":"O43683","full_name":"Mitotic checkpoint serine/threonine-protein kinase BUB1","aliases":["BUB1A"],"length_aa":1085,"mass_kda":122.4,"function":"Serine/threonine-protein kinase that performs 2 crucial functions during mitosis: it is essential for spindle-assembly checkpoint signaling and for correct chromosome alignment. Has a key role in the assembly of checkpoint proteins at the kinetochore, being required for the subsequent localization of CENPF, BUB1B, CENPE and MAD2L1. Required for the kinetochore localization of PLK1. Required for centromeric enrichment of AUKRB in prometaphase. Plays an important role in defining SGO1 localization and thereby affects sister chromatid cohesion. Promotes the centromeric localization of TOP2A (PubMed:35044816). Acts as a substrate for anaphase-promoting complex or cyclosome (APC/C) in complex with its activator CDH1 (APC/C-Cdh1). Necessary for ensuring proper chromosome segregation and binding to BUB3 is essential for this function. Can regulate chromosome segregation in a kinetochore-independent manner. Can phosphorylate BUB3. The BUB1-BUB3 complex plays a role in the inhibition of APC/C when spindle-assembly checkpoint is activated and inhibits the ubiquitin ligase activity of APC/C by phosphorylating its activator CDC20. This complex can also phosphorylate MAD1L1. Kinase activity is essential for inhibition of APC/CCDC20 and for chromosome alignment but does not play a major role in the spindle-assembly checkpoint activity. Mediates cell death in response to chromosome missegregation and acts to suppress spontaneous tumorigenesis","subcellular_location":"Nucleus; Chromosome, centromere, kinetochore","url":"https://www.uniprot.org/uniprotkb/O43683/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/BUB1","classification":"Common Essential","n_dependent_lines":944,"n_total_lines":1208,"dependency_fraction":0.7814569536423841},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000169679","cell_line_id":"CID001136","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"ANAPC4","stoichiometry":0.2},{"gene":"DDOST","stoichiometry":0.2},{"gene":"FKBP5","stoichiometry":0.2},{"gene":"OST4","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001136","total_profiled":1310},"omim":[{"mim_id":"620183","title":"MICROCEPHALY 30, PRIMARY, AUTOSOMAL RECESSIVE; MCPH30","url":"https://www.omim.org/entry/620183"},{"mim_id":"619247","title":"SPINDLE- AND KINETOCHORE-ASSOCIATED COMPLEX, SUBUNIT 3; SKA3","url":"https://www.omim.org/entry/619247"},{"mim_id":"614560","title":"MAU2 SISTER CHROMATID COHESION FACTOR; MAU2","url":"https://www.omim.org/entry/614560"},{"mim_id":"614030","title":"SPEEDY/RINGO CELL CYCLE REGULATOR FAMILY, MEMBER C; SPDYC","url":"https://www.omim.org/entry/614030"},{"mim_id":"613499","title":"HISTONE GENE CLUSTER 1, H2A HISTONE FAMILY, MEMBER A; HIST1H2AA","url":"https://www.omim.org/entry/613499"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":11.2},{"tissue":"lymphoid tissue","ntpm":25.6},{"tissue":"testis","ntpm":28.3}],"url":"https://www.proteinatlas.org/search/BUB1"},"hgnc":{"alias_symbol":["hBUB1","BUB1A"],"prev_symbol":["BUB1L"]},"alphafold":{"accession":"O43683","domains":[{"cath_id":"1.25.40.430","chopping":"5-147","consensus_level":"medium","plddt":86.609,"start":5,"end":147},{"cath_id":"1.10.510.10","chopping":"744-841_852-868","consensus_level":"medium","plddt":89.7896,"start":744,"end":868},{"cath_id":"1.10.510.10","chopping":"870-1085","consensus_level":"medium","plddt":90.4291,"start":870,"end":1085}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43683","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43683-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43683-F1-predicted_aligned_error_v6.png","plddt_mean":62.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=BUB1","jax_strain_url":"https://www.jax.org/strain/search?query=BUB1"},"sequence":{"accession":"O43683","fasta_url":"https://rest.uniprot.org/uniprotkb/O43683.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43683/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43683"}},"corpus_meta":[{"pmid":"9182760","id":"PMC_9182760","title":"Kinetochore 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dominant-negative in mammalian cells with specific mitotic phenotype, foundational paper with 480 citations\",\n      \"pmids\": [\"9182760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"hBUB1 first appears at kinetochores during early prophase before hBUBR1; both kinases concentrate at the outer kinetochore plate and co-localize with CENP-E, suggesting they monitor kinetochore-microtubule interactions.\",\n      \"method\": \"Immunofluorescence, immunoelectron microscopy, antibody localization\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by immunoelectron microscopy with functional context, replicated across studies\",\n      \"pmids\": [\"9914370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Fission yeast Bub1 is recruited to centromeres upon spindle checkpoint activation and is essential for the checkpoint response to spindle damage and centromere defects; loss of bub1 causes chromosome lagging and increased chromosome loss in unperturbed mitosis.\",\n      \"method\": \"Gene deletion, immunofluorescence, live imaging\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with defined cellular phenotypes, ortholog in fission yeast\",\n      \"pmids\": [\"9864354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"BUB1 and BUB3 form a complex of monomers that interacts with MAD1; this multiprotein complex exhibits kinase activity requiring Lys821 in the BUB1 kinase motif, resulting in BUB1 autophosphorylation and phosphorylation of associated MAD1.\",\n      \"method\": \"In vitro kinase assay, co-immunoprecipitation, site-directed mutagenesis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay with mutagenesis, single study\",\n      \"pmids\": [\"10198256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Bub1 localizes to kinetochores during meiosis I and II in Xenopus oocytes; its electrophoretic mobility shifts (reflecting phosphorylation and activation) during meiosis I, and this activation is MAPK-dependent and can be induced by p90(Rsk), which phosphorylates Bub1 in vitro and increases its kinase activity.\",\n      \"method\": \"In vitro kinase assay, immunofluorescence, MEK inhibitor (U0126), injection of constitutively active p90Rsk\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation plus in vivo reconstitution with multiple orthogonal approaches\",\n      \"pmids\": [\"11231148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In mammalian cells, Bub1 and BubR1 are recruited to kinetochores in response to loss of tension (low-dose vinblastine) but not microtubule detachment, while Mad2 responds to attachment loss; Mad2 does not associate with Bub1 or BubR1, indicating they operate in distinct checkpoint pathways.\",\n      \"method\": \"Immunofluorescence with microtubule toxins at defined doses, co-immunoprecipitation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods distinguishing tension vs. attachment pathways\",\n      \"pmids\": [\"11274370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Bub1 and BubR1 are part of a common complex during mitosis; Bub1 localization is sensitive to both tension and microtubule attachment (asymmetric at kinetochores, dependent on microtubule attachment), while BubR1 localization is symmetrical; Bub1 is rapidly phosphorylated by nocodazole or taxol treatment.\",\n      \"method\": \"Immunofluorescence, cell synchronization, microtubule toxin treatment\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic localization studies with functional context, single lab\",\n      \"pmids\": [\"11792804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Fission yeast Bub1 is essential for the meiotic pattern of chromosome segregation: Bub1 deletion causes sister kinetochores to disunite at MI and prevents retention of Rec8 cohesin at centromeres at anaphase I, revealing roles in sister kinetochore co-orientation and centromeric cohesion beyond spindle checkpoint.\",\n      \"method\": \"Gene deletion, live imaging, immunofluorescence\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with multiple defined meiotic phenotypes, ortholog\",\n      \"pmids\": [\"11331883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Immunodepletion of Bub1 from Xenopus egg extracts blocks Mos-dependent establishment of CSF arrest; rescue requires wild-type but not kinase-dead Bub1, demonstrating that Bub1 kinase activity is required for establishment of meiotic metaphase arrest and APC inhibition downstream of MAPK/Rsk.\",\n      \"method\": \"Immunodepletion from egg extracts, kinase-dead rescue, in vitro reconstitution\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in egg extracts with kinase-dead mutant rescue\",\n      \"pmids\": [\"12123578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Bub1 directly phosphorylates Cdc20 in vitro and catalytically inhibits APC/C(Cdc20) ubiquitin ligase activity; a Cdc20 mutant with all six Bub1 phosphorylation sites removed is refractory to inhibition; upon checkpoint activation, Bub1 kinase activity toward Cdc20 is stimulated; expression of non-phosphorylatable Cdc20 allows mitotic exit despite spindle damage.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, APC/C ubiquitination assay, RNAi in HeLa cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis plus cellular rescue, multiple orthogonal methods\",\n      \"pmids\": [\"15525512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Xenopus Bub1 is hyperphosphorylated and activated on unattached chromosomes; MAPK phosphorylates Bub1 at consensus sites and is required for this activation; activated Bub1 enhances checkpoint efficiency and promotes recruitment of other checkpoint proteins to kinetochores.\",\n      \"method\": \"In vitro kinase assay, MAPK inhibition, site-directed mutagenesis, checkpoint assay in Xenopus\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with mutagenesis and cellular validation\",\n      \"pmids\": [\"15241477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Human Bub1 is required for centromeric localization of Sgo1 (shugoshin) during mitosis; Bub1 depletion causes Sgo1 to redistribute along chromosome arms and leads to loosening of centromeric cohesion.\",\n      \"method\": \"RNAi knockdown, immunofluorescence, live-cell imaging\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — RNAi with specific localization and functional cohesion phenotype, replicated in subsequent studies\",\n      \"pmids\": [\"15723797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Bub1 depletion leads to accumulation of misaligned chromatids with both sister kinetochores linked to microtubules abnormally; Bub1 and Aurora B are recruited to kinetochores independently of each other and have additive effects when co-depleted, indicating parallel pathways for stable bipolar kinetochore-microtubule attachment.\",\n      \"method\": \"RNAi, live-cell imaging, fluorescence microscopy, double-depletion epistasis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis by double depletion with defined cellular phenotype\",\n      \"pmids\": [\"15933723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Plk1 binds Bub1 through its polo-box domain (PBD) in mitotic cells; this interaction requires Cdk1-mediated phosphorylation of Bub1 at T609; Bub1 depletion diminishes kinetochore localization of Plk1, and expression of wild-type but not T609A Bub1 restores Plk1 kinetochore localization.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis, RNAi, immunofluorescence, in vitro kinase assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal pulldown with mutagenesis and cellular rescue experiment\",\n      \"pmids\": [\"16760428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Bub1 is degraded during mitotic exit by APC/C(Cdh1) through two KEN-box motifs; mutation of both KEN boxes stabilizes Bub1 in cells; Bub1 is ubiquitinated by immunopurified APC/C(Cdh1) in vitro.\",\n      \"method\": \"In vitro ubiquitination assay, site-directed mutagenesis, RNAi of Cdh1, protein stability assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ubiquitination reconstitution plus mutagenesis and cellular validation\",\n      \"pmids\": [\"17158872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Budding yeast Bub1 kinase domain is required for accurate chromosome biorientation after nocodazole release; Bub1 kinase mislocalizes Sgo1p when absent, and both kinase domain and Sgo1 are required for efficient biorientation.\",\n      \"method\": \"Kinase-domain deletion, live imaging, immunofluorescence, genetic epistasis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with epistasis and defined phenotype, ortholog\",\n      \"pmids\": [\"18081426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In fission yeast, Bub1 acts as a stable kinetochore scaffold (confirmed by FRAP); tethering Bub1 to telomeres is sufficient to recruit anaphase inhibitors (Mad2, Mad3) in a kinase-independent manner.\",\n      \"method\": \"FRAP, ectopic tethering to telomeres, kinetochore recruitment assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — FRAP plus gain-of-function tethering with functional readout, ortholog\",\n      \"pmids\": [\"18094750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"BUB1 depletion in normal human fibroblasts via RNAi triggers premature senescence dependent on p53 and its target p21(CIP1); cells with reduced Bub1 and inactivated p53 become highly aneuploid, revealing a surveillance mechanism linking Bub1 loss to the p53 pathway.\",\n      \"method\": \"RNAi knockdown, dominant-negative p53, p21 depletion, senescence assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via double knockdown/dominant-negative with specific phenotypic readout\",\n      \"pmids\": [\"17488820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structure of the Bub1 kinase domain reveals an N-terminal extension required for kinase activity; the activation segment has active-kinase features but its C-terminal portion sterically restricts substrate access; Bub1 uses KEN-box docking motifs outside the kinase domain to recruit Cdc20, and these KEN boxes are required for spindle checkpoint function in human cells.\",\n      \"method\": \"X-ray crystallography, mutagenesis, in vitro kinase assay, checkpoint assay in HeLa cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation by mutagenesis and cellular assay\",\n      \"pmids\": [\"18995837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SV40 large T antigen binds Bub1 directly; T antigen coimmunoprecipitates with endogenous Bub1 and Bub3; spindle checkpoint override by T antigen depends on Bub1 binding, and T antigen-induced tetraploidy and DNA damage response (p53 stabilization via ATM/ATR) are also Bub1-binding dependent.\",\n      \"method\": \"Co-immunoprecipitation, genetic analysis (T antigen mutants), DNA damage markers\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — Co-IP with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"18922873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Bub1 phosphorylates the conserved serine 121 of histone H2A in fission yeast; this phosphorylation is required for centromeric localization of shugoshin proteins; h2a-SA mutant phenocopies bub1 kinase-dead mutant; artificial tethering of shugoshin to centromeres rescues CIN defects in both h2a-SA and bub1-KD mutants.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, ectopic tethering rescue, genetic epistasis\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis, epistasis, and functional rescue, replicated across labs\",\n      \"pmids\": [\"19965387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the N-terminal TPR region of BUB1 at 1.74 Å resolution; functional mutagenesis identifies residues important for interaction with the kinetochore protein Blinkin (KNL1), which is required for kinetochore localization and function of BUB1 in the SAC.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, in vivo localization assay\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional mutagenesis validation\",\n      \"pmids\": [\"19141287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In oocytes, Bub1 controls APC/C activation timing: Bub1 deletion accelerates APC/C-mediated securin destruction by ~5 hours; Bub1's kinase domain is not required for this APC/C delay; premature chiasmata resolution in Bub1-deficient oocytes requires APC/C and separase activity.\",\n      \"method\": \"Cre-lox conditional oocyte knockout, quantitative APC/C activity assay, genetic epistasis with Apc2 and separase\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional knockout with quantitative biochemical readout and genetic epistasis\",\n      \"pmids\": [\"19249208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Sgo1 is first recruited to centromeric heterochromatin in G2 in an HP1-dependent but Bub1-kinase-independent manner; during prophase, Sgo1 centromeric re-localization requires Bub1 kinase activity; Bub1 kinase activity is not required for checkpoint function or chromosome alignment in mammalian cells using BUB1-null MEF complementation.\",\n      \"method\": \"Null MEF complementation with kinase-dead Bub1, live-cell imaging, immunofluorescence across cell cycle stages\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null MEF complementation with kinase-dead Bub1, multiple orthogonal observations\",\n      \"pmids\": [\"20124418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Bub1 overexpression in mice causes aberrant kinase activity and hyperactivation of Aurora B kinase, leading to chromosome misalignment/lagging and aneuploidy; pharmacological or genetic (BubR1 overexpression) suppression of Aurora B corrects these errors, placing Aurora B downstream of Bub1 overexpression.\",\n      \"method\": \"Transgenic mouse overexpression, Aurora B inhibition, epistasis by BubR1 overexpression, live imaging\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic model with pharmacological and genetic epistasis\",\n      \"pmids\": [\"21646403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mps1 is the major kinase copurifying with yeast kinetochore particles and phosphorylates conserved MELT motifs in Spc105/KNL1; this phosphorylation recruits Bub1 to kinetochores and is reversed by PP1; Spc105 mutants lacking MELT phosphorylation sites are checkpoint-defective.\",\n      \"method\": \"Kinetochore particle purification, in vitro kinase assay, phosphosite mutagenesis, checkpoint assay\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis and checkpoint functional readout, replicated by parallel study\",\n      \"pmids\": [\"22521787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mps1 (Mph1) phosphorylation of MELT motifs in Spc7 (KNL1 ortholog) recruits Bub1 and Bub3 to kinetochores in fission yeast, and this recruitment is required to maintain SAC signaling.\",\n      \"method\": \"Phosphosite mutagenesis, kinetochore recruitment assay, checkpoint assay\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic mutagenesis with functional checkpoint readout, replicated by parallel study\",\n      \"pmids\": [\"22521786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of Bub1 TPR domain in complex with KNL1 KI motif; interaction occurs along the convex TPR surface; point mutations on this surface impair Bub1-KNL1 interaction in vitro and in vivo; a 62-residue segment C-terminal to the TPRs including the Bub3-binding domain is necessary and largely sufficient for kinetochore recruitment.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, in vitro binding, in vivo kinetochore localization assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis with in vivo validation\",\n      \"pmids\": [\"22331848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Bub1 kinase activity drives error correction and mitotic checkpoint signaling in mice via phosphorylation of histone H2A at T121, which controls Aurora B kinase localization and activity; mice lacking Bub1 kinase activity show substantial chromosome segregation errors but no increased tumor susceptibility.\",\n      \"method\": \"Knockin mouse (kinase-dead), H2A-T121 phosphorylation assay, Aurora B localization, tumor analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockin mouse model with multiple defined molecular and cellular readouts\",\n      \"pmids\": [\"23209306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mad1 kinetochore localization in budding yeast is mediated by Mps1 phosphorylation of a conserved region within Bub1; tethering this Bub1 region to kinetochores bypasses the need for upstream checkpoint recruitment of Mps1; the Mad1 interaction with Bub1 and kinetochores can be reconstituted with Mps1 and Mad2 in vitro.\",\n      \"method\": \"Reconstitution in vitro, kinetochore tethering bypass, checkpoint genetics\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus bypass tethering experiment\",\n      \"pmids\": [\"24402315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Phosphorylation at the P+1 loop of human Bub1 enhances its activity specifically toward H2A but not Cdc20; crystal structure of phosphorylated Bub1 reveals phosphorylation-triggered reorganization of the P+1 loop; this activating phosphorylation occurs constitutively during the cell cycle and appears to be intramolecular autophosphorylation; enrichment of H2A-pT120 at mitotic kinetochores requires kinetochore targeting of Bub1.\",\n      \"method\": \"X-ray crystallography, in vitro kinase assay, substrate-specific phosphorylation, mutagenesis\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus in vitro kinase assay with mutagenesis\",\n      \"pmids\": [\"25308863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"BuGZ binds and stabilizes Bub3 during interphase and mitosis through its GLEBS domain; BuGZ inhibition causes loss of both Bub3 and Bub1 from kinetochores, reduction of Bub1-dependent H2A phosphorylation at centromeres, and attenuation of Aurora B activity, leading to chromosome congression defects.\",\n      \"method\": \"RNAi, co-immunoprecipitation, immunofluorescence, phosphorylation assay\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional cascade with multiple readouts, single lab\",\n      \"pmids\": [\"24462187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Bub1 and BubR1 heterodimerize with each other at a pseudo-symmetric interface; Bub1 (but not BubR1) enhances Bub3 binding to phosphorylated kinetochores; grafting a short Bub1 motif onto BubR1 promotes Bub1-independent kinetochore recruitment of BubR1 but cannot sustain a functional checkpoint; kinetochore localization of BubR1 requires direct heterodimerization with Bub1.\",\n      \"method\": \"Structural analysis, in vitro binding, mutagenesis, gain-of-function chimera, checkpoint assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — structure plus multiple functional assays demonstrating mechanism of sub-functionalization\",\n      \"pmids\": [\"25611342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Bub1 kinase activity promotes TGF-β signaling: Bub1 interacts with TGFBRI and TGFBRII forming a ternary complex, promotes receptor heterodimerization, and is required for SMAD3 recruitment, SMAD2/3 phosphorylation, and SMAD-dependent transcription; a kinase-dead Bub1 mutant and small-molecule inhibitor (2OH-BNPP1) suppress TGF-β signaling.\",\n      \"method\": \"RNAi kinome screen, co-immunoprecipitation, kinase-dead mutant, small-molecule inhibitor, in vivo xenograft\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, kinase-dead, inhibitor, in vivo) showing mechanistic pathway role\",\n      \"pmids\": [\"25564677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human BUB1 contributes to SAC signaling through a 50-amino-acid segment containing an ABBA motif and KEN box that promotes efficient CDC20 binding at kinetochores; kinetochore recruitment of BUBR1 and BUB3 by BUB1 is dispensable for SAC activation; human BUB1 does not stably associate with MAD1.\",\n      \"method\": \"Domain deletion/mutagenesis, complementation, checkpoint assay, Co-IP\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mutagenesis with rescue and checkpoint functional readout\",\n      \"pmids\": [\"26148513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Distinct domains within Bub1 mediate kinetochore recruitment of RZZ complex and BubR1 separately; the middle region of Bub1 contributes to RZZ localization; a distinct region mediates BubR1 kinetochore localization through direct binding; removal of the BubR1-recruiting region paradoxically increases checkpoint strength.\",\n      \"method\": \"Domain deletion, Co-IP, immunofluorescence, checkpoint assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with functional checkpoint phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"26031201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Bub1 autophosphorylation at T589 controls kinetochore turnover of Bub1; T589A mutation causes uniform H2A-T120 phosphorylation along chromosome arms and aberrant Sgo1 recruitment; kinetochore tethering of Bub1-T589A refocuses H2A-T120 phosphorylation to centromeres, linking Bub1 kinetochore docking to localized H2A phosphorylation.\",\n      \"method\": \"Quantitative phosphoproteomics, autophosphorylation assay, site-directed mutagenesis, kinetochore tethering\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — phosphoproteomics plus mutagenesis and tethering rescue\",\n      \"pmids\": [\"26399325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Bub1 inhibition (BAY-320 and BAY-524) reduces shugoshin and chromosomal passenger complex (CPC/Aurora B) chromosomal association, impairs chromosome arm resolution, and sensitizes cells to paclitaxel; Bub1 inhibition has only minor effects on mitotic progression or SAC function, distinguishing scaffolding from catalytic roles.\",\n      \"method\": \"Small-molecule kinase inhibitors (BAY-320, BAY-524), immunofluorescence, mitotic timing assay, drug combination assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — potent selective inhibitors with multiple readouts comparing inhibition vs. depletion phenotypes\",\n      \"pmids\": [\"26885717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Bub1 scaffolds Plk1-mediated phosphorylation of Cdc20; Bub1-Plk1-dependent Cdc20 phosphorylation inhibits APC/C(Cdc20) in vitro, is required for checkpoint signaling in human cells, and acts in a parallel pathway to MCC formation; a phospho-mimicking Cdc20 mutant restores mitotic arrest in Mad2 or BubR1-depleted cells.\",\n      \"method\": \"In vitro APC/C assay, Co-IP, RNAi, phospho-mimetic rescue, checkpoint assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro APC/C assay with mutagenesis and genetic epistasis\",\n      \"pmids\": [\"26912231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In fission yeast, multisite binding of Bub3 to the Spc7 MELT array toggles the spindle checkpoint switch by permitting Mph1 (Mps1)-dependent interaction of Bub1 with Mad1-Mad2.\",\n      \"method\": \"Phosphosite mutagenesis, checkpoint functional assay, Co-IP\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic/biochemical mechanism in yeast ortholog, single study\",\n      \"pmids\": [\"27618268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In fission yeast meiosis, Moa1 (meikin) recruits Plo1 (polo-like kinase) to kinetochores to phosphorylate Spc7 (KNL1) and accumulate Bub1, causing meiotic Bub1 to persist at kinetochores until anaphase I; this ensures robust Sgo1 localization and centromeric cohesion protection; this meiosis-specific Bub1 regulation is conserved in mouse.\",\n      \"method\": \"Genetic analysis, immunofluorescence, kinase assay, mouse meiosis analysis\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with mechanistic biochemical evidence, ortholog\",\n      \"pmids\": [\"28497540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The BUB3-BUB1 complex binds to telomeres during S phase and promotes telomere DNA replication; loss of the complex causes fragile and shortened telomeres; TRF2 targets BUB1-BUB3 to telomeres; BUB1 directly phosphorylates TRF1 to promote recruitment of BLM helicase for resolution of replication stress.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, chromatin fractionation, telomere replication assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay with Co-IP and functional telomere replication readout\",\n      \"pmids\": [\"29727616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Malonylation of histone H2A at K119 inhibits the interaction between Bub1 and H2A, reducing Bub1-dependent H2A-S121 phosphorylation in vitro and causing loss of shugoshin chromosomal localization; anionic mutations at K119 phenocopy this in yeast.\",\n      \"method\": \"In vitro peptide binding assay, in vitro kinase assay, site-directed mutagenesis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assay with mutagenesis, single study\",\n      \"pmids\": [\"29769606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In human cells, RZZ's sole role in SAC activation is to tether Mad1-Mad2 to kinetochores; Bub1 and KNL1 activate kinetochore-bound Mad1-Mad2 to produce a 'wait anaphase' signal but are not required for fibrous corona formation; Mps1 phosphorylates Rod to trigger corona formation independently of Bub1.\",\n      \"method\": \"Genome editing (BUB1 disruption), RNAi, checkpoint assay, immunofluorescence\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — complete genetic removal via genome editing with multiple functional readouts\",\n      \"pmids\": [\"30415700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Efficient spindle checkpoint signaling requires integrated activities of Bub1 and the RZZ complex; Rod removal reduces proximity of Bub1 and Mad1; bypassing Rod requirement by tethering Mad1 or strengthening Bub1-Mad1 interaction is sufficient; Bub1 has checkpoint functions independent of Mad1 localization, suggesting a catalytic role.\",\n      \"method\": \"Genome editing + RNAi, proximity ligation assay, tethering bypass, checkpoint assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome editing with tethering bypass and multiple functional readouts\",\n      \"pmids\": [\"30782962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Either Haspin or Bub1 activity is sufficient to recruit Aurora B to distinct chromosomal loci; joint inhibition of both kinases fully abolishes Aurora B accumulation at centromeres, impairing correction of erroneous KT-MT attachments; Aurora B substrates at the kinetochore (Hec1, Dsn1, Knl1) are phosphorylated independently of centromere-localized Aurora B pools.\",\n      \"method\": \"Kinase inhibition (single and combined), immunofluorescence, chromosome segregation assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double kinase inhibition epistasis with multiple molecular readouts\",\n      \"pmids\": [\"32027339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Aurora B kinase directly promotes MCC production by working downstream of Mps1 in budding yeast and human cells; conditional dimerization of Aurora B with Bub1 (but not with the Spc105 phosphodomain) leads to ectopic MCC production; Bub1 must recruit both Mad1 and Cdc20 for this signaling; Aurora B cooperates with Bub1 after Mps1 licenses Bub1 recruitment.\",\n      \"method\": \"Ectopic SAC activation (eSAC) system, conditional dimerization, checkpoint assay in yeast and HeLa cells\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function tethering system with epistasis in two organisms\",\n      \"pmids\": [\"34861183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"BUB1 directly interacts with STAT3 and mediates phosphorylation of STAT3 at Ser727; pharmacological inhibition of BUB1 kinase activity or BUB1 kinase-domain mutation abrogates STAT3 transcriptional activation; BUB1 kinase inhibition suppresses bladder cancer cell growth in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, kinase-dead mutant, pharmacological inhibitor, xenograft\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with kinase-dead mutant and inhibitor, single lab\",\n      \"pmids\": [\"34852826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Crystal structure of Mad1 C-terminal domain bound to two phosphorylated Bub1 CD1 peptides at 1.75 Å; phosphorylated Bub1 Thr461 interacts with Arg617 of the Mad1 RLK motif and acts as N-terminal cap to the CD1 α-helix dipole; only one Bub1 CD1 peptide binds the Mad1 homodimer in solution due to inherent asymmetry in the Mad1 coiled-coil.\",\n      \"method\": \"X-ray crystallography, NMR, solution binding assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with solution binding validation\",\n      \"pmids\": [\"34013668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mps1 phosphorylation of both Bub1 CD1 and Mad1 CTD generates a tripartite assembly of Bub1 and Cdc20 on Mad1 CTD; this positions Cdc20's Mad2-interacting motif (MIM) near open-Mad2 to catalyze C-Mad2:Cdc20 formation and MCC assembly.\",\n      \"method\": \"X-ray crystallography, cross-linking mass spectrometry, in vitro reconstitution of MCC assembly\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural and biochemical reconstitution with multiple orthogonal methods\",\n      \"pmids\": [\"36289199\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"BUB1 is a multifunctional serine/threonine kinase that (1) localizes to kinetochores via its N-terminal TPR domain binding to phospho-MELT motifs of KNL1/Spc105 (phosphorylated by Mps1/Mph1), where it acts as a scaffold recruiting BubR1, BUB3, RZZ, and Mad1-Mad2 for spindle assembly checkpoint (SAC) signaling; (2) directly phosphorylates histone H2A at T120/S121 to recruit shugoshin proteins and thereby protect centromeric cohesion; (3) phosphorylates and inhibits the APC/C activator Cdc20 (both directly and by scaffolding Plk1), and is itself degraded by APC/C(Cdh1) via KEN-box motifs; (4) recruits Plk1 to kinetochores via a Cdk1-phospho-T609 docking site; (5) cooperates with Aurora B and Haspin to generate the inner centromere Aurora B pool that corrects erroneous kinetochore-microtubule attachments; and (6) has roles beyond mitosis including promotion of TGF-β receptor signaling, telomere replication via TRF2-dependent recruitment and TRF1 phosphorylation, and DNA damage response activation through ATM-mediated phosphorylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"BUB1 is a conserved serine/threonine kinase that functions as a central kinetochore scaffold and catalytic hub coordinating spindle assembly checkpoint (SAC) signaling, chromosome biorientation, and centromeric cohesion protection during cell division. BUB1 is recruited to kinetochores via its N-terminal TPR domain binding Mps1-phosphorylated MELT motifs on KNL1/Spc105, where it scaffolds recruitment of BubR1, RZZ, and Mad1–Mad2 through distinct domains, and positions Cdc20 on Mad1 to catalyze mitotic checkpoint complex (MCC) assembly [PMID:25611342, PMID:36289199, PMID:22521787]. Its kinase activity phosphorylates histone H2A at T120/S121 to recruit shugoshin proteins for centromeric cohesion protection and to localize Aurora B for error correction of kinetochore–microtubule attachments, while it also directly and indirectly (via Plk1 scaffolding) phosphorylates Cdc20 to inhibit APC/C [PMID:19965387, PMID:15525512, PMID:26912231, PMID:23209306]. Beyond mitosis, BUB1 promotes TGF-β receptor signaling by facilitating receptor heterodimerization and SMAD phosphorylation, and supports telomere replication by phosphorylating TRF1 downstream of TRF2-dependent recruitment [PMID:25564677, PMID:29727616].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing BUB1 as a kinetochore-localized kinase required for the spindle assembly checkpoint answered the foundational question of whether vertebrate cells use checkpoint kinases analogous to yeast Bub1.\",\n      \"evidence\": \"Dominant-negative mutant expression and immunofluorescence in mammalian cells\",\n      \"pmids\": [\"9182760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous substrates unknown\", \"Mechanism of kinetochore recruitment undefined\", \"Relationship to BubR1 not established\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Localization studies resolved when and where BUB1 acts: it arrives at outer kinetochores in early prophase before BubR1, and in fission yeast is essential for both checkpoint response and accurate chromosome segregation in unperturbed mitosis.\",\n      \"evidence\": \"Immunoelectron microscopy in human cells; gene deletion in fission yeast with live imaging\",\n      \"pmids\": [\"9914370\", \"9864354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of kinetochore targeting still unknown\", \"No structural information on BUB1 domains\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Multiple studies established that BUB1 has functions beyond checkpoint signaling: it is required for meiotic sister kinetochore co-orientation and centromeric cohesion protection in fission yeast, and is activated by the MAPK/p90Rsk pathway during meiosis.\",\n      \"evidence\": \"Gene deletion in fission yeast meiosis; kinase assays and MEK inhibition in Xenopus oocytes\",\n      \"pmids\": [\"11331883\", \"11231148\", \"11274370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate linking BUB1 to cohesion protection not identified\", \"Mechanism of MAPK-mediated activation unclear structurally\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of Cdc20 as a direct BUB1 kinase substrate explained how BUB1 catalytic activity inhibits APC/C: phosphorylation of six Cdc20 sites blocks APC/C activation, and non-phosphorylatable Cdc20 permits mitotic exit despite spindle damage.\",\n      \"evidence\": \"In vitro kinase and APC/C ubiquitination assays with site-directed mutagenesis; RNAi in HeLa cells\",\n      \"pmids\": [\"15525512\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Cdc20 phosphorylation is sufficient for checkpoint in vivo uncertain\", \"Other catalytic substrates not yet identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that BUB1 is required for centromeric localization of shugoshin (Sgo1) and for accurate bipolar kinetochore–microtubule attachment linked BUB1 to cohesion protection and error correction pathways distinct from its checkpoint role.\",\n      \"evidence\": \"RNAi in human cells with localization and cohesion phenotypes; epistasis with Aurora B\",\n      \"pmids\": [\"15723797\", \"15933723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct BUB1 substrate mediating Sgo1 recruitment unknown\", \"Mechanism of parallel action with Aurora B not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"BUB1 was shown to recruit Plk1 to kinetochores via Cdk1-phosphorylated T609, and to be degraded by APC/C(Cdh1) through KEN-box motifs, establishing BUB1 as both a scaffold for Plk1 and a regulated APC/C substrate.\",\n      \"evidence\": \"Reciprocal Co-IP with T609A mutagenesis; in vitro ubiquitination by APC/C(Cdh1) with KEN-box mutagenesis\",\n      \"pmids\": [\"16760428\", \"17158872\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of Plk1 recruitment via BUB1 not yet defined\", \"How KEN boxes coordinate Cdc20 binding vs. APC/C-mediated degradation unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Crystal structure of the BUB1 kinase domain revealed an N-terminal extension required for activity and showed that BUB1 uses KEN-box motifs to dock Cdc20 for checkpoint signaling, resolving how a single kinase accomplishes both catalytic and scaffolding functions.\",\n      \"evidence\": \"X-ray crystallography with mutagenesis and checkpoint assay in HeLa cells\",\n      \"pmids\": [\"18995837\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate selectivity mechanism not resolved\", \"How kinase domain activation segment restricts access unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of histone H2A S121 (T120 in mammals) as the direct BUB1 kinase substrate responsible for shugoshin recruitment answered a long-standing question about the molecular mechanism connecting BUB1 kinase activity to cohesion protection.\",\n      \"evidence\": \"In vitro kinase assay, h2a-SA mutagenesis phenocopying bub1-KD, ectopic tethering rescue in fission yeast\",\n      \"pmids\": [\"19965387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of H2A recognition by BUB1 unknown\", \"Whether this mechanism is fully conserved in mammals not yet confirmed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The crystal structure of BUB1's TPR domain and its interaction with KNL1 defined the structural basis of BUB1 kinetochore recruitment, answering how BUB1 docks at unattached kinetochores.\",\n      \"evidence\": \"X-ray crystallography at 1.74 Å with functional mutagenesis and localization assay\",\n      \"pmids\": [\"19141287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How phospho-MELT recognition integrates with TPR–KI interaction not yet clear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Parallel studies in budding and fission yeast established that Mps1 phosphorylation of MELT motifs on KNL1/Spc105 is the signal that recruits BUB1–BUB3, explaining the upstream regulation of BUB1 kinetochore targeting and linking it to unattached kinetochore status.\",\n      \"evidence\": \"Kinetochore particle purification, in vitro kinase assay, phosphosite mutagenesis in S. cerevisiae and S. pombe\",\n      \"pmids\": [\"22521787\", \"22521786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Valency and cooperativity of multi-MELT engagement not yet quantified\", \"PP1 reversal kinetics not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"A kinase-dead knockin mouse demonstrated that BUB1 kinase activity drives H2A-T121 phosphorylation, Aurora B centromeric localization, and error correction in vivo, but is dispensable for tumor suppression, separating catalytic from scaffolding functions in a mammalian organism.\",\n      \"evidence\": \"Knockin mouse model with H2A-T121 phosphorylation and Aurora B localization assays\",\n      \"pmids\": [\"23209306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why kinase-dead mice lack tumor susceptibility despite segregation errors is unexplained\", \"Contribution of scaffolding vs. kinase to SAC not fully delineated in vivo\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Domain mapping in human BUB1 resolved how a single scaffold protein recruits distinct checkpoint effectors: separate domains mediate BubR1 heterodimerization, RZZ recruitment, and Cdc20 binding (via ABBA motif and KEN box), while BUB1 enhances BUB3 phospho-MELT binding to explain why BubR1 depends on BUB1 for kinetochore access.\",\n      \"evidence\": \"Structural analysis, domain deletion, chimeric constructs, checkpoint and localization assays\",\n      \"pmids\": [\"25611342\", \"26031201\", \"26148513\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How removal of BubR1-recruiting domain increases checkpoint strength is paradoxical and unexplained\", \"Stoichiometry of BUB1 scaffold complexes at kinetochores undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that BUB1 promotes TGF-β signaling by forming a ternary complex with TGF-β receptors and facilitating SMAD phosphorylation established a non-mitotic function for BUB1 kinase activity in a major signaling pathway.\",\n      \"evidence\": \"RNAi kinome screen, Co-IP, kinase-dead mutant, small-molecule inhibitor, xenograft model\",\n      \"pmids\": [\"25564677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct BUB1 phosphorylation target in TGF-β pathway not identified\", \"How cytoplasmic TGF-β signaling interfaces with kinetochore BUB1 pool unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Selective BUB1 kinase inhibitors (BAY-320/BAY-524) confirmed that catalytic activity is specifically required for shugoshin and Aurora B chromosomal localization but has only minor effects on SAC function, definitively separating kinase-dependent from scaffold-dependent roles.\",\n      \"evidence\": \"Small-molecule kinase inhibitors with immunofluorescence, mitotic timing, and drug combination assays\",\n      \"pmids\": [\"26885717\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether kinase inhibition sensitizes tumors to taxanes in patients untested\", \"Off-target effects not fully excluded\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"BUB1 was shown to scaffold Plk1-mediated phosphorylation of Cdc20 as a parallel APC/C inhibitory mechanism alongside MCC formation, resolving the functional consequence of the BUB1-Plk1 interaction discovered a decade earlier.\",\n      \"evidence\": \"In vitro APC/C assay, RNAi, phospho-mimetic Cdc20 rescue of Mad2/BubR1-depleted cells\",\n      \"pmids\": [\"26912231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of direct BUB1 vs. BUB1-scaffolded Plk1 phosphorylation of Cdc20 not quantified in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"BUB1–BUB3 was found to localize to telomeres during S phase via TRF2 and phosphorylate TRF1 to recruit BLM helicase for replication stress resolution, establishing a replication function entirely outside mitosis.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay, chromatin fractionation, telomere replication assay\",\n      \"pmids\": [\"29727616\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"BUB1 phosphosite(s) on TRF1 not mapped\", \"Whether telomere shortening phenotype is kinase-dependent not fully tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Combined inhibition of BUB1 and Haspin fully abolished centromeric Aurora B accumulation, demonstrating that two parallel histone-mark pathways converge to position the chromosomal passenger complex for error correction.\",\n      \"evidence\": \"Single and combined kinase inhibition with immunofluorescence and segregation assays\",\n      \"pmids\": [\"32027339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Aurora B at other loci compensates for centromeric loss not fully resolved\", \"Quantitative contribution of each pathway varies by cell type\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Structural reconstitution of the Mps1-phosphorylated Bub1–Cdc20–Mad1 CTD tripartite complex explained the catalytic mechanism of MCC assembly: Bub1 and Cdc20 are co-positioned on Mad1 to present Cdc20's Mad2-interacting motif near open-Mad2, resolving the long-sought template model for checkpoint signal generation.\",\n      \"evidence\": \"X-ray crystallography, cross-linking mass spectrometry, in vitro MCC reconstitution\",\n      \"pmids\": [\"36289199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How kinetochore geometry and valency modulate catalytic rate not determined\", \"Full-length reconstitution of the signaling cascade from Mps1 through MCC not achieved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how BUB1's mitotic and interphase pools are differentially regulated, the structural basis for substrate selectivity between H2A and Cdc20, quantitative contributions of BUB1's scaffold versus kinase activities to SAC robustness in human tissues, and whether BUB1 kinase inhibition has therapeutic utility.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length BUB1 structure\", \"No in vivo quantitative model integrating all BUB1 activities\", \"Therapeutic window for BUB1 kinase inhibition not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 9, 20, 30, 33, 41, 47]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [16, 32, 35, 38]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [20, 30, 42]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 1, 2, 25, 27, 28]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 9, 25, 28, 37, 49]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [33]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [41]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [20, 30, 42]}\n    ],\n    \"complexes\": [\n      \"BUB1–BUB3\",\n      \"MCC (mitotic checkpoint complex)\"\n    ],\n    \"partners\": [\n      \"BUB3\",\n      \"BUBR1\",\n      \"MAD1\",\n      \"CDC20\",\n      \"KNL1\",\n      \"PLK1\",\n      \"SGO1\",\n      \"TRF2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}