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Showing BABAM1 — MERIT40 is a alias.

BABAM1

BRISC and BRCA1-A complex member 1 · UniProt Q9NWV8

Length
329 aa
Mass
36.6 kDa
Annotated
2026-06-09
16 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/6 claims corpus-supported (83%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

BABAM1 (NBA1/MERIT40) is a core structural subunit of the BRCA1-A complex that organizes ubiquitin-directed DNA double-strand break (DSB) signaling and links it to homologous recombination and the broader DNA damage response (PMID:19261749, PMID:19261746). It is incorporated into the RAP80/Abraxas/BRCC36/BRE-containing complex through a direct C-terminal interaction with BRE/BRCC45 and through contacts with the adaptor ABRAXAS, where it functions as a scaffolding/bridging element that stabilizes the assembly and maintains the protein abundance of BRE and Abraxas (PMID:19261748, PMID:21282113, PMID:24125081, PMID:24667604). By preserving complex integrity, BABAM1 is required for RAP80-directed retention of BRCA1 at DSBs, for the Lys63-deubiquitinase activity of BRCC36, and for the G2/M checkpoint and ionizing-radiation resistance (PMID:19261749, PMID:19261746); the same C-terminal BRE-binding motif also sustains the cytoplasmic ABRO1-BRCC36 complex (PMID:21282113). Beyond DSB repair, BABAM1 acts upstream of FANCD2 in interstrand cross-link repair, where Merit40-null cells show delayed ICL unhooking, reduced end resection, and reduced recombination (PMID:26338419), and it recruits Tankyrase1 to DSBs via an N-terminal RXXPEG/tankyrase-binding motif to promote homologous recombination and proper mitotic spindle assembly, an activity restrained by WWOX (PMID:30533199, PMID:30571846, PMID:37248434). Its repair function is tuned by phosphorylation: Akt phosphorylates BABAM1 to promote BRCA1-A complex assembly after genotoxic stress, and mTORC2 controls BABAM1 Ser29 phosphorylation to sustain nuclear DNA repair activity (PMID:26027929, PMID:36315652). Independently of DSB repair, BABAM1 is a subunit of an Lnk-associated Lys63-deubiquitinating complex that attenuates hematopoietic stem cell expansion through a Tpo/Mpl signaling axis (PMID:25636339).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2009 High

    Establishing that an uncharacterized protein is a bona fide BRCA1-A complex subunit answered whether BRCA1 recruitment to damage sites depends on a dedicated stabilizing factor.

    Evidence Genetic screen and reciprocal proteomics with localization and knockdown checkpoint/IR-resistance readouts, replicated across three labs

    PMID:19261746 PMID:19261748 PMID:19261749

    Open questions at the time
    • Did not resolve which subunit BABAM1 directly contacts
    • Mechanism by which it maintains BRE/Abraxas abundance not defined
  2. 2011 High

    Mapping the BABAM1-BRE interface defined the molecular basis for complex stabilization and revealed a role beyond the nuclear complex.

    Evidence Co-IP with domain mapping/mutagenesis tying the NBA1 C-terminal motif to the BRE UEV domain, plus functional IR/BRCA1-foci readouts

    PMID:21282113

    Open questions at the time
    • Functional consequences of disrupting the cytoplasmic ABRO1-BRCC36 complex not separated from nuclear effects
  3. 2013 Medium

    Biophysical characterization addressed how BABAM1 acts structurally, showing it dimerizes and presents a vWA-like core that bridges complex members.

    Evidence Recombinant protein purification, unfolding spectroscopy/calorimetry, modeling, and ABRAXAS binding assays

    PMID:24125081 PMID:24667604

    Open questions at the time
    • No high-resolution structure of the assembled complex
    • Functional relevance of dimerization in cells untested
  4. 2015 High

    In vivo knockout work distinguished BABAM1's DSB role from a distinct requirement in interstrand cross-link repair upstream of FANCD2.

    Evidence Merit40-null mice with ICL sensitivity assays, repair foci, and genetic epistasis against Brca2 and Fancd2

    PMID:26338419

    Open questions at the time
    • Molecular mechanism linking the BRCA1-A complex to ICL unhooking not defined
    • How BABAM1 acts upstream of FANCD2 unclear
  5. 2015 High

    Hematopoietic studies revealed a DSB-repair-independent role as a subunit of an Lnk-associated K63-DUB complex restraining stem cell expansion.

    Evidence Knockout mice with serial transplantation, Tpo stimulation, and M40 x Mpl epistasis

    PMID:25636339

    Open questions at the time
    • DUB substrates relevant to Tpo/Mpl signaling not identified
    • Relationship to the BRCA1-A complex in HSCs unresolved
  6. 2015 Medium

    Identifying Akt phosphorylation addressed how BABAM1-dependent complex assembly is activated by genotoxic stress.

    Evidence In vitro kinase assay, phospho-specific antibody, Co-IP, and inhibitor-coupled survival assays

    PMID:26027929

    Open questions at the time
    • Phosphosite-to-assembly mechanism not structurally defined
    • Not independently replicated
  7. 2018 Medium

    Discovery of a tankyrase-binding motif showed BABAM1 recruits Tankyrase1 to DSBs, extending its function to PARP-family signaling at breaks.

    Evidence LC-MS/MS, Co-IP, mutagenesis, and IR-sensitivity rescue with a binding-deficient mutant

    PMID:30533199

    Open questions at the time
    • Downstream consequence of tankyrase recruitment at breaks not fully defined
    • Single lab
  8. 2019 Medium

    Defining the RXXPEG/ARC-V interface linked BABAM1-Tankyrase1 binding to mitotic spindle assembly and chromosome alignment.

    Evidence R28A mutagenesis, Co-IP, and mitotic phenotype analysis

    PMID:30571846

    Open questions at the time
    • Spindle role not connected mechanistically to the DSB-repair function
    • Single study
  9. 2022 Medium

    Placing BABAM1 Ser29 phosphorylation under mTORC2 control identified an additional kinase input governing its nuclear repair activity.

    Evidence Quantitative phosphoproteomics with mTORC2 inhibition, nuclear fractionation, and apoptosis/γH2AX readouts in glioblastoma cells

    PMID:36315652

    Open questions at the time
    • Direct vs indirect mTORC2 phosphorylation not established
    • Relationship between Ser29 and the Akt site unresolved
  10. 2023 Medium

    Identifying WWOX as a negative regulator showed how excessive BABAM1-Tankyrase-driven recombination is restrained.

    Evidence Co-IP, HR reporter assays, and interaction-disruption experiments

    PMID:37248434

    Open questions at the time
    • Structural basis of WWOX interference with the BABAM1-Tankyrase interface unknown
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • How BABAM1's multiple kinase inputs, tankyrase-dependent functions, and DUB-complex roles are integrated and coordinated across nuclear repair, mitosis, and hematopoiesis remains unresolved.
  • No unified model linking Akt and mTORC2 phosphorylation to specific outputs
  • Substrates of the BABAM1-containing DUB complexes in different tissues unidentified
  • No high-resolution structure of BABAM1 within an assembled complex

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4 GO:0005198 structural molecule activity 2
Localization
GO:0005634 nucleus 3 GO:0005829 cytosol 1
Pathway
R-HSA-73894 DNA Repair 3 R-HSA-1640170 Cell Cycle 1
Partners
ABRAXASBRCA1BRCC36BRERAP80TNKS1WWOX
Complex memberships
ABRO1-BRCC36 complexAbraxas-BRCC36 complexBRCA1-A complexLnk-associated K63-deubiquitinating complex

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2009 NBA1/MERIT40 is a component of the BRCA1 A complex (containing BRCA1/BARD1, Abraxas, RAP80, BRCC36, and BRE), is required for resistance to ionizing radiation, localizes to DNA damage sites, maintains BRE and Abraxas protein abundance, and is required for recruitment of BRCA1 to DNA damage sites. Four members of the BRCA1-A complex possess polyubiquitin chain-binding capability. Genetic screen, proteomic analysis, protein localization (live imaging/foci), knockdown with phenotypic readout (IR resistance, G2/M checkpoint) Genes & development High 19261749
2009 MERIT40 directly interacts with BRE/BRCC45 and is assembled into the RAP80/Abraxas-containing BRCA1 complex via this interaction. MERIT40 regulates BRCA1 retention at DNA breaks and checkpoint function primarily by maintaining the stability of BRE and the five-subunit complex. Co-immunoprecipitation, protein stability assays, knockdown with DNA damage foci and checkpoint readouts Genes & development High 19261748
2009 MERIT40 is essential for BRCA1-Rap80 complex protein interactions, stability, and DSB targeting. MERIT40 is required for Rap80-associated Lys63-ubiquitin deubiquitinase (BRCC36 DUB) activity, and for G2 checkpoint and viability responses to ionizing radiation. Co-immunoprecipitation, knockdown, DUB activity assay, IR sensitivity assay, DNA damage foci Genes & development High 19261746
2011 NBA1/MERIT40 interacts with BRE through a C-terminal conserved motif of NBA1 and the C-terminal UEV domain of BRE, and this interaction is critical for maintaining the integrity of both the nuclear Abraxas-BRCC36 complex and the cytoplasmic ABRO1-BRCC36 complex. Knockdown of NBA1 decreases protein levels of components in both complexes and impairs BRCA1 recruitment to damage sites. Co-immunoprecipitation, domain mapping/mutagenesis, knockdown with functional readouts (IR resistance, BRCA1 foci) The Journal of biological chemistry High 21282113
2015 MERIT40 is phosphorylated by Akt following doxorubicin-induced DNA damage. This Akt-mediated phosphorylation of MERIT40 facilitates assembly of the BRCA1-A complex in response to DNA damage and contributes to DNA repair and cell survival. In vitro kinase assay, phospho-specific antibody, co-immunoprecipitation, cell survival assays with PI3K/Akt inhibitors Cell reports Medium 26027929
2015 MERIT40 is required for ICL (interstrand cross-link) repair: Merit40-null mice show hypersensitivity to ICLs but not whole-body irradiation. MERIT40 is recruited to ICL lesions prior to FANCD2, and Merit40-null cells exhibit delayed ICL unhooking, reduced end resection, and reduced homologous recombination at ICL damage. Merit40 mutation exacerbated ICL-induced chromosome instability with Brca2 deficiency but not with Fancd2 mutation, defining its epistatic relationship within the FA-BRCA network. Knockout mouse model, ICL sensitivity assays, DNA repair foci (FANCD2, RAD51), chromosomal instability assays, genetic epistasis Genes & development High 26338419
2015 MERIT40 is a core subunit of an Lnk-associated Lys63 deubiquitinating complex that attenuates HSC expansion. Loss of MERIT40 increases HSC pool size, enhances resistance to cytoablative stress, and increases repopulating ability and self-renewal. M40-null HSCs show hypersensitivity to thrombopoietin (Tpo) stimulation, and HSC phenotypes are abrogated on a Tpo receptor (Mpl)-null background. Knockout mouse model, serial transplantation, Tpo stimulation assays, genetic epistasis (M40 x Mpl double KO) Blood High 25636339
2018 MERIT40 directly binds Tankyrase (PARP family) via a tankyrase-binding consensus motif, and recruits tankyrase to DNA double-strand break sites following X-ray irradiation. Cells expressing a tankyrase-binding-deficient MERIT40 mutant fail to rescue the IR-sensitivity phenotype of MERIT40 knockdown cells. LC-MS/MS, co-immunoprecipitation, mutagenesis, DNA damage foci, IR sensitivity assay with rescue Oncotarget Medium 30533199
2019 The RXXPEG motif of MERIT40 mediates direct interaction with the ARC-V domain of Tankyrase1 (TNKS1). Mutation of RXXPEG (R28A) disrupts MERIT40-TNKS1 interaction and causes aberrant spindle assembly and chromosome misalignment, demonstrating a role for MERIT40 in spindle structure/function through TNKS1. Mutagenesis (R28A), co-immunoprecipitation, mitotic phenotype analysis (spindle assembly, chromosome alignment) Cell biology international Medium 30571846
2022 BABAM1 phosphorylation at Ser29 is regulated by mTORC2 in glioblastoma cells. Inhibition of mTORC2 reduces pBABAM1(Ser29), decreases DNA repair activity in the nucleus, and promotes apoptosis. mTORC2 also controls γH2AX levels. These findings place BABAM1 as an mTORC2 downstream effector in the DNA damage response. Quantitative phosphoproteomic analysis, mTORC2 inhibition (pharmacological), phospho-specific readouts (pBABAM1-Ser29, γH2AX), nuclear fractionation, apoptosis assays Journal of proteome research Medium 36315652
2013 MERIT40 forms a dimer in a concentration-independent manner and contains a stable central domain with structural similarity to vWA-like regions. MERIT40 interacts with ABRAXAS (the adaptor molecule of the BRCA1 complex), helping to bridge and stabilize the complex. Recombinant protein purification, spectroscopic/calorimetric unfolding assays, molecular modeling, limited proteolysis, pulldown/binding assay Journal of biomolecular structure & dynamics Medium 24125081
2014 MERIT40 interacts with ABRAXAS in a non-phosphorylation-dependent manner via the BRCA1-BRCT domain region, acting as an adapter molecule that generates a scaffold among complex members to stabilize the BRCA1-A complex. Recombinant protein purification, direct binding/pulldown assay, spectroscopic characterization Biochemical and biophysical research communications Medium 24667604
2023 WWOX physically interacts with MERIT40 and inhibits excessive homologous recombination (HR) activity induced by MERIT40 overexpression. WWOX impairs the MERIT40-Tankyrase interaction, preventing the MERIT40-Tankyrase complex from promoting HR at DSBs. Co-immunoprecipitation (WWOX-MERIT40 interaction), HR reporter assay, overexpression/knockdown with functional readouts Cancer gene therapy Medium 37248434

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 NBA1, a new player in the Brca1 A complex, is required for DNA damage resistance and checkpoint control. Genes & development 143 19261749
2009 MERIT40 facilitates BRCA1 localization and DNA damage repair. Genes & development 132 19261748
2009 MERIT40 controls BRCA1-Rap80 complex integrity and recruitment to DNA double-strand breaks. Genes & development 125 19261746
2011 NBA1/MERIT40 and BRE interaction is required for the integrity of two distinct deubiquitinating enzyme BRCC36-containing complexes. The Journal of biological chemistry 62 21282113
2015 MERIT40 Is an Akt Substrate that Promotes Resolution of DNA Damage Induced by Chemotherapy. Cell reports 41 26027929
2015 MERIT40 cooperates with BRCA2 to resolve DNA interstrand cross-links. Genes & development 25 26338419
2018 MERIT40-dependent recruitment of tankyrase to damaged DNA and its implication for cell sensitivity to DNA-damaging anticancer drugs. Oncotarget 18 30533199
2009 Mutation screening of the MERIT40 gene encoding a novel BRCA1 and RAP80 interacting protein in breast cancer families. Breast cancer research and treatment 11 19572197
2022 Phosphoproteomic Analysis Defines BABAM1 as mTORC2 Downstream Effector Promoting DNA Damage Response in Glioblastoma Cells. Journal of proteome research 9 36315652
2015 MERIT40 deficiency expands hematopoietic stem cell pools by regulating thrombopoietin receptor signaling. Blood 8 25636339
2014 Role of MERIT40 in stabilization of BRCA1 complex: a protein-protein interaction study. Biochemical and biophysical research communications 7 24667604
2023 WWOX binds MERIT40 and modulates its function in homologous recombination, implications in breast cancer. Cancer gene therapy 6 37248434
2013 Structural and functional characterization of the MERIT40 to understand its role in DNA repair. Journal of biomolecular structure & dynamics 5 24125081
2019 RXXPEG motif of MERIT40 is required to maintain spindle structure and function through its interaction with Tankyrase1. Cell biology international 4 30571846
2017 Regulation of macrophage migration in ischemic mouse hearts via an AKT2/NBA1/SPK1 pathway. Oncotarget 1 29383164
2011 Germline mutational analysis of the C19orf62 gene in African-American women with breast cancer. Breast cancer research and treatment 0 21431873

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