Affinage

HUS1

Checkpoint protein HUS1 · UniProt O60921

Length
280 aa
Mass
31.7 kDa
Annotated
2026-06-10
90 papers in source corpus 51 papers cited in narrative 50 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/7 claims corpus-supported (86%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HUS1 is a subunit of the heterotrimeric RAD9-RAD1-HUS1 (9-1-1) checkpoint clamp, a PCNA-like toroidal ring that functions at the interface of DNA damage signaling and DNA repair to safeguard genome stability (PMID:9872989, PMID:10871397, PMID:19446481, PMID:19535328). In response to replication stress and genotoxin exposure, the 9-1-1 ring is loaded onto damaged chromatin in an RPA-dependent, replication-coupled but kinase-independent manner, requiring the RAD17 clamp loader; this loading is a proximal event that does not depend on ATM, ATR, or DNA-PK catalytic activity (PMID:12015327, PMID:12228248, PMID:15897895). Once chromatin-bound, 9-1-1 scaffolds ATR-mediated CHK1 activation by recruiting TopBP1 through CK2-phosphorylated serines in the RAD9 C-terminal tail, localizing TopBP1's ATR-activation domain to stalled forks; this RAD9-TopBP1 contact can be functionally bypassed by tethering the activation domain to chromatin, establishing localization as the clamp's core signaling role (PMID:17575048, PMID:17636252, PMID:20545769). HUS1 function is genetically required upstream of CHK1 and for the S-phase checkpoint response to replication-blocking lesions, and its loss causes embryonic lethality, spontaneous chromosomal instability, and telomere shortening (PMID:10921903, PMID:11790307, PMID:12529385, PMID:16890531). Independently of its signaling role, 9-1-1 acts as a direct stimulator of base excision repair, binding and activating glycosylases and downstream enzymes including MYH, NEIL1, TDG, OGG1, APE1, DNA polymerase beta, FEN1, and DNA ligase I through subunit-specific contacts mapped to the interdomain-connecting loops and outer-surface pockets of the clamp (PMID:15314187, PMID:15556996, PMID:16731526, PMID:16879101, PMID:17395641, PMID:17426133, PMID:19615952). Crystal and EM structures define 9-1-1 as a double-faced ring whose unique surfaces, distinct from PCNA, mediate repair-enzyme docking and partner binding such as RHINO on the back face (PMID:19446481, PMID:19535328, PMID:31776186). HUS1 also contributes to homologous recombination, meiotic DSB repair, and the survival of BRCA2-deficient cells via gap suppression [PMID:16278671, PMID:23468651, PMID:bio_10.1101_2025.10.07.680950].

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 1999 High

    Established that HUS1 is not a standalone protein but a stable partner of RAD1 and RAD9, defining the heterotrimeric complex that would become the unit of study.

    Evidence Reciprocal co-immunoprecipitation from human cell lysates

    PMID:9872989

    Open questions at the time
    • Stoichiometry and architecture of the complex not defined
    • Functional role of the complex not yet established
  2. 2000 Medium

    Predicted the structural logic of the complex — that the three subunits each fold like PCNA and assemble into a sliding-clamp ring loaded by a RFC-like RAD17 — providing the mechanistic framework for all subsequent work.

    Evidence Computational fold recognition and comparative modeling

    PMID:10871397

    Open questions at the time
    • Purely predictive, awaited crystallographic validation
    • Subunit order within the ring inferred, not measured
  3. 2000 High

    Demonstrated in mice that Hus1 is essential for genome stability and for specific genotoxin responses, distinguishing replication-stress/UV responses from the ionizing-radiation response.

    Evidence Targeted gene disruption in mouse with chromosome analysis and clonogenic survival

    PMID:10648611 PMID:10921903

    Open questions at the time
    • Molecular basis of genotoxin selectivity unresolved
    • Whether lethality reflects checkpoint vs repair functions unclear
  4. 2002 High

    Placed Hus1 upstream of Chk1, separate from Chk2/p53, establishing the 9-1-1 complex as a dedicated branch of damage signaling, and showed chromatin loading depends on RPA and replication initiation but not on checkpoint kinases.

    Evidence Mouse KO with retroviral rescue, Xenopus egg extract chromatin fractionation, pharmacological kinase inhibition; C. elegans loss-of-function genetics

    PMID:11790307 PMID:12015327 PMID:12228248 PMID:12445383 PMID:12529385

    Open questions at the time
    • How loaded 9-1-1 transmits signal to ATR/Chk1 not yet defined
    • Direct partners mediating signaling unidentified
  5. 2005 High

    Identified RPA as the direct partner that couples 9-1-1 chromatin recruitment to ssDNA, explaining the RPA-dependence of loading.

    Evidence Reciprocal Co-IP, GST pulldown subunit mapping, siRNA, chromatin fractionation in human cells

    PMID:15897895

    Open questions at the time
    • Order of RPA binding relative to RAD17-dependent loading not fully resolved
    • Whether RPA contact is required after loading unclear
  6. 2007 High

    Resolved the central mechanism of checkpoint signaling: the clamp recruits TopBP1 via the phosphorylated RAD9 C-tail to deliver TopBP1's ATR-activation domain to stalled forks, a role bypassable by direct AD tethering.

    Evidence Domain-swap fusion complementation in human cells, Xenopus egg extract phosphomutant and dominant-negative analysis

    PMID:17575048 PMID:17636252

    Open questions at the time
    • Kinase responsible for the activating RAD9 phosphorylation not yet assigned
    • Regulation of the RAD9 tail availability undefined
  7. 2010 High

    Defined the upstream control of the TopBP1 interaction — RAD17 ATPase activity for loading/recruitment and CK2 phosphorylation of RAD9 Ser-341/387 — and uncovered ATR phosphorylation of HUS1 itself as a distinct signaling readout.

    Evidence Xenopus extract with RAD17 ATPase mutants, in vitro CK2 kinase assay with phosphomutants and clonogenic survival, phosphosite mapping

    PMID:16436514 PMID:20110345 PMID:20545769

    Open questions at the time
    • Function of ATR-phosphorylated HUS1 S219/T223 not established
    • How CK2 phosphorylation is spatially regulated unclear
  8. 2009 High

    Provided atomic and structural validation of the PCNA-like ring while revealing the unique IDC loops and a single, p21-competable repair-enzyme docking site that distinguish 9-1-1 from PCNA.

    Evidence X-ray crystallography of human 9-1-1, co-crystal with FEN1 PIP-box, DNA-binding EMSA

    PMID:19446481 PMID:19464297 PMID:19535328

    Open questions at the time
    • How a single site accommodates many repair partners in vivo unclear
    • Conformational dynamics on DNA not captured
  9. 2009 High

    Established 9-1-1's second major function as a direct activator of base excision repair, binding and stimulating a broad set of glycosylases and BER enzymes through subunit-specific and IDC-loop contacts.

    Evidence In vitro reconstitution, binding/activity assays and interaction mapping for pol beta, FEN1, ligase I, MYH, NEIL1, TDG, OGG1, APE1

    PMID:15314187 PMID:15556996 PMID:16216273 PMID:16731526 PMID:16879101 PMID:17395641 PMID:17426133 PMID:17855402 PMID:19615952

    Open questions at the time
    • In vivo contribution of each stimulation relative to PCNA unquantified
    • How the clamp coordinates sequential BER steps on one site unresolved
  10. 2015 High

    Mapped HUS1-specific functional surfaces, separating its roles in complex assembly/DNA loading and ATR signaling from its hydrophobic-pocket-mediated MYH binding and damage survival.

    Evidence Systematic site-directed mutagenesis with chromatin fractionation, Co-IP, clonogenic survival, Chk1 phospho-blots; IDC-loop and DNA-binding mapping

    PMID:20816984 PMID:25911100 PMID:26021743

    Open questions at the time
    • Whether separable surfaces act simultaneously in vivo unknown
    • Higher-order regulation of surface accessibility undefined
  11. 2019 High

    Revealed 9-1-1 as a functionally double-faced clamp, with partners such as RHINO binding the back/edge of the ring through RAD1, expanding the scaffolding capacity beyond the front face.

    Evidence X-ray crystallography of 9-1-1 bound to a RHINO peptide

    PMID:31776186

    Open questions at the time
    • Functional consequence of RHINO back-face binding for signaling not defined here
    • Whether both faces are engaged simultaneously unknown
  12. 2024 Medium

    Extended 9-1-1's roles to DSB end resection and BRCA2-deficient cell survival, showing redundancy with MRN in Dna2 resection and a role in suppressing PRIMPOL-dependent ssDNA gap degradation.

    Evidence Xenopus egg extract resection assays with immunodepletion; genome-wide CRISPR screen with EXO1/PRIMPOL epistasis and ssDNA gap assays (preprint)

    PMID:38349040 PMID:bio_10.1101_2025.10.07.680950

    Open questions at the time
    • BRCA2 gap-suppression mechanism rests on a non-peer-reviewed preprint
    • Direct molecular role of 9-1-1 in POLzeta gap filling not biochemically defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the two arms of 9-1-1 function — checkpoint scaffolding versus direct repair-enzyme stimulation — are coordinated or switched at a single damage site in vivo remains unresolved.
  • No in vivo measurement of competition among repair partners at the single docking site
  • Temporal switching between signaling and repair modes undefined
  • Physiological hierarchy of the many in vitro stimulations unquantified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 7 GO:0060090 molecular adaptor activity 4 GO:0003677 DNA binding 2 GO:0005198 structural molecule activity 2
Localization
GO:0000228 nuclear chromosome 4 GO:0005634 nucleus 3 GO:0005654 nucleoplasm 3
Pathway
R-HSA-73894 DNA Repair 7 R-HSA-1640170 Cell Cycle 5 R-HSA-8953897 Cellular responses to stimuli 4 R-HSA-69306 DNA Replication 3
Partners
FEN1MYHRAD1RAD17RAD9ARHINORPATOPBP1
Complex memberships
9-1-1 complex (RAD9-RAD1-HUS1)

Evidence

Reading pass · 50 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 Human HUS1 (hHus1) forms a heterotrimeric complex with hRad1 and hRad9 in human cells; hRad9 undergoes phosphorylation in response to DNA damage and is a key participant in complex formation. Co-immunoprecipitation from human cell lysates The Journal of biological chemistry High 9872989
2000 Computational fold recognition and comparative modeling predicted that Rad1, Hus1, and Rad9 each adopt a PCNA-like fold and together form a heterotrimeric ring structure, with Rad17 acting as a clamp loader analogous to RFC. The order of subunits within the ring was predicted. Computational fold recognition, comparative modeling, generalized sequence profiles Nucleic acids research Medium 10871397
2000 S. pombe Hus1 associates with Rad9 and Rad1 in a protein complex (the 9-1-1 complex); Hus1 is phosphorylated basally and further phosphorylated after irradiation. Nuclear localization of Hus1 depends on Rad17. MYC-tagged co-immunoprecipitation, indirect immunofluorescence, cell fractionation Molecular and cellular biology High 10648611
2000 Mouse Hus1 inactivation causes embryonic lethality, spontaneous chromosomal abnormalities, and impaired Chk1-dependent responses to hydroxyurea and UV, but only mildly increased sensitivity to ionizing radiation, establishing Hus1 as essential for genomic stability and specific genotoxin responses. Targeted gene disruption in mouse, chromosome analysis, clonogenic survival assays Genes & development High 10921903
2001 Structure-function analysis of fission yeast Hus1-Rad1-Rad9 complex showed that PCNA alignment identifies some functionally important residues, but the complex also possesses unique structural and functional features not explained by the PCNA model. Site-directed mutagenesis, checkpoint functional assays in S. pombe Molecular biology of the cell Medium 11739777
2002 Mouse Hus1 acts upstream of Chk1 in the DNA damage signaling pathway: Hus1-null cells show greatly reduced genotoxin-induced Chk1 phosphorylation, which is restored by retroviral Hus1 complementation. Chk2 phosphorylation and p53 accumulation after damage are Hus1-independent. Genetic KO with retroviral complementation, Western blot for Chk1/Chk2 phosphorylation Current biology : CB High 11790307
2002 In Xenopus egg extracts, Hus1 (Xhus1) is required for checkpoint-dependent Chk1 phosphorylation and associates with chromatin in an initiation-dependent, RPA-dependent, and polymerase-alpha-dependent manner, independently of XATR chromatin association. Nucleus-free DNA replication system, chromatin fractionation, depletion experiments in Xenopus egg extracts The Journal of biological chemistry High 12015327
2002 C. elegans HUS-1 relocalizes to distinct chromatin foci following DNA damage, is required for DNA damage-induced cell cycle arrest and apoptosis, maintains genome stability (prevents chromosome nondisjunction and telomere shortening), and promotes p53/CEP-1-dependent transcription of the pro-apoptotic gene egl-1. Loss-of-function genetics in C. elegans, immunofluorescence, mutation frequency assays, epistasis with cep-1/p53 Current biology : CB High 12445383
2002 Genotoxin-induced chromatin loading of the 9-1-1 complex does not require ATM, ATR, or DNA-PK catalytic activity, and does not require DNA replication, demonstrating that 9-1-1 chromatin binding is a proximal, kinase-independent event in checkpoint signaling. Chromatin fractionation, pharmacological kinase inhibition, cell-cycle block experiments The Journal of biological chemistry High 12228248
2003 Mouse Hus1 is specifically required for the S-phase DNA damage checkpoint in response to bulky DNA adducts (BPDE), but not for the ionizing radiation-responsive S-phase checkpoint (which requires NBS1), demonstrating two separable S-phase checkpoint pathways. Targeted KO of mouse Hus1 and Nbs1, DNA synthesis assays after genotoxin treatment Molecular and cellular biology High 12529385
2004 The human 9-1-1 complex physically interacts with DNA polymerase beta in vitro and stimulates its activity, increasing its affinity for primer-template, stimulating dNTP misincorporation, and enhancing strand displacement synthesis on 1-nt gap substrates. This stimulation is specific to pol beta and not pol lambda, pol alpha, or pol delta. In vitro co-immunoprecipitation, DNA polymerase activity assays Nucleic acids research High 15314187
2004 The human 9-1-1 complex binds and stimulates flap endonuclease 1 (FEN1) on flap, nick, and gapped substrates simulating repair intermediates. Stimulation partially requires access to double-stranded DNA ends. Unlike PCNA, 9-1-1 does not substitute for PCNA in stimulating DNA pol beta. In vitro binding and nuclease activity assays, substrate competition experiments Proceedings of the National Academy of Sciences of the United States of America High 15556996
2004 ATR, Claspin, Rad9, and Hus1 regulate Chk1 phosphorylation and Cdc25A stability during physiological S phase in the absence of exogenous DNA damage; siRNA depletion of Hus1 stabilizes Cdc25A, indicating the ATR-9-1-1-Chk1-Cdc25A pathway operates constitutively during S phase. siRNA knockdown, Western blot for Chk1 phosphorylation and Cdc25A levels Cell cycle (Georgetown, Tex.) High 15190204
2004 Rad17 and Hus1 are required for HIV-1 Vpr-mediated G2 arrest; Vpr activates the ATR-dependent checkpoint pathway requiring these factors, and induces γ-H2AX phosphorylation and nuclear BRCA1 foci formation. siRNA knockdown, cell cycle analysis, immunofluorescence Molecular and cellular biology Medium 15485898
2004 S. pombe MYH (MutY homolog) physically interacts with all three subunits of the 9-1-1 complex (SpRad9/SpRad1/SpHus1) in yeast extracts and when individually expressed in bacteria. The SpHus1-SpMYH interaction increases after hydrogen peroxide treatment and correlates with SpHus1 phosphorylation. SpMYH associates with SpHus1 in a ~450 kDa complex. Co-immunoprecipitation, bacterial expression, gel filtration, phosphorylation analysis The Journal of biological chemistry High 15533944
2004 Hus1-deficient mouse cells show an impaired S-phase checkpoint after camptothecin (≥1 µM) or high-dose ionizing radiation (≥15 Gy) reflecting primarily the chain elongation step of DNA replication, correlated with reduced dissociation of PCNA from replication foci. Chk1 and ATR activation were normal at doses where the checkpoint defect was manifest. Hus1-KO mouse cells, DNA synthesis assays, PCNA foci analysis by immunofluorescence Nucleic acids research Medium 14762204
2005 The 9-1-1 complex directly interacts with RPA in human cells; this interaction is mediated by Rad9 binding to RPA70 and RPA32 subunits. UV or camptothecin treatment stimulates the 9-1-1/RPA interaction and colocalization. RPA knockdown blocks damage-dependent 9-1-1 chromatin association and disrupts 9-1-1 complex formation. Co-immunoprecipitation, GST pulldown, siRNA knockdown, immunofluorescence colocalization, chromatin fractionation Oncogene High 15897895
2005 The 9-1-1 complex interacts with and specifically stimulates DNA ligase I; this interaction can be immunoprecipitated from human cells and is enhanced by UV irradiation. 9-1-1 improves DNA ligase I binding to nicked dsDNA and stimulates ligation on both linear and circular substrates (unlike PCNA), suggesting a non-encirclement-based stimulation mechanism. Co-immunoprecipitation from human cells, in vitro ligation assays on varied substrates, DNA binding assays The Journal of biological chemistry High 16731526
2005 PCNA and the 9-1-1 complex independently bind to and activate FEN1. Acetylation of FEN1 by p300-HAT abolishes 9-1-1-mediated stimulation but does not affect PCNA-mediated stimulation, indicating a differential regulatory mechanism. In vitro FEN1 activity assays, acetylation by p300-HAT, binding competition Journal of molecular biology High 16216273
2006 Human MYH interacts with hHus1 and hRad1 (but not hRad9). The major Hus1-binding site on hMYH maps to residues 295–350; Val315 of hMYH is critical for the Hus1 interaction. hHus1 and the S. pombe 9-1-1 complex enhance the glycosylase activity of SpMYH. The hMYH–hHus1 interaction is enhanced by ionizing radiation. Co-immunoprecipitation, GST pulldown with deletion mutants, site-directed mutagenesis, in vitro glycosylase activity assay, immunofluorescence The Biochemical journal High 16879101
2006 The mammalian 9-1-1 (Rad9/Rad1/Hus1) complex localizes to telomeres in human and mouse cells, and Hus1-deficient MEFs and thymocytes show severe telomere shortening. The 9-1-1 complex co-purifies with catalytically active telomerase and positively regulates its DNA polymerase activity. ChIP/telomere-associated fraction, quantitative telomere length measurement (Q-FISH/Southern), co-purification with telomerase activity assay Current biology : CB High 16890531
2006 Hus1 loss increases sensitivity to ionizing radiation through impairment of homologous recombination repair (HRR), but is independent of non-homologous end-joining (NHEJ) — cells show similar DSB induction and rejoining rates but reduced HRR efficiency measured by I-SceI assay. Clonogenic survival assay, pulsed-field gel electrophoresis for DSBs, I-SceI–based HRR assay, siRNA knockdown Oncogene High 16278671
2007 Rad9's role in Chk1 activation is to bind TopBP1, which stimulates ATR-mediated Chk1 phosphorylation via TopBP1's ATR-activation domain (AD). Fusion of the AD to PCNA or histone H2B bypasses the requirement for the 9-1-1 clamp, indicating the 9-1-1 clamp's primary role is to localize the AD to stalled replication forks. Genetic epistasis in human cells, fusion protein complementation assays, siRNA Genes & development High 17575048
2007 In Xenopus egg extracts, TopBP1 binds the 9-1-1 complex via its BRCT I-II region, which interacts with the C-terminal domain of Rad9; this binding requires phosphorylation of Rad9 Ser-373. Mutant TopBP1 lacking BRCT I-II or Rad9 with Ala at Ser-373 impairs checkpoint signaling; an isolated Rad9 C-terminal fragment acts as a dominant-negative inhibitor of checkpoint signaling. Xenopus egg extract immunodepletion, phosphomutant analysis, dominant-negative fragment inhibition, checkpoint assay The Journal of biological chemistry High 17636252
2007 The 9-1-1 complex interacts with and stimulates NEIL1 glycosylase activity. Residues 290–350 of hNEIL1 are important for 9-1-1 association. Individual subunits hHus1, hRad1, and hRad9 each stimulate NEIL1 glycosylase activity. NEIL1 and Rad9 nuclear foci colocalize in hydrogen peroxide–treated cells. Co-immunoprecipitation, GST pulldown with deletion mutants, in vitro glycosylase assay, immunofluorescence Nucleic acids research High 17395641
2007 The 9-1-1 complex physically interacts with and stimulates hTDG glycosylase. The hHus1-interacting domain maps to residues 67–110 of hTDG (Val74 is critical). The TDG-Rad9 interaction is enhanced after MNNG treatment. TDG and Rad9 foci colocalize in methylating-agent–treated cells. Co-immunoprecipitation, GST pulldown, deletion and point mutagenesis, in vitro glycosylase assay, immunofluorescence Nucleic acids research High 17855402
2007 Jab1 physically associates with the 9-1-1 complex via direct interaction with Rad1 subunit, causes nuclear-to-cytoplasmic translocation of the 9-1-1 complex, and promotes its degradation via the 26S proteasome. Jab1 overexpression suppresses checkpoint signaling and DNA synthesis recovery after replication stress. Co-immunoprecipitation, subcellular fractionation, proteasome inhibitor, functional checkpoint assays Journal of molecular biology Medium 17583730
2007 Drosophila hus1 is required for S-phase checkpoint activation in somatic cells, for meiotic checkpoint activation, and for organization of oocyte DNA (possibly independent of meiotic checkpoint). hus1 mutant females are sterile and the flies are sensitive to HU and MMS but not X-rays, and G2/M checkpoint is intact. Null allele by P-element excision, survival assays, cell cycle analysis, oocyte imaging Journal of cell science High 17327271
2007 The 9-1-1 complex interacts with and stimulates APE1 AP-endonuclease activity in vitro and in vivo; it also preferentially stimulates the early components APE1 and DNA pol beta in a long-patch BER reconstitution assay, suggesting a hierarchy of interactions in the BER repairosome. In vitro co-immunoprecipitation, AP-endonuclease activity assay, LP-BER reconstitution in vitro Nucleic acids research High 17426133
2008 Loss of Hus1 sensitizes cells to etoposide-induced apoptosis by upregulating BH3-only proteins Bim and Puma. In Hus1-deficient cells, Rad9 relocates to the cytoplasm where it binds Bcl-2, augmenting mitochondrial apoptosis. Hus1 KO mouse cells, siRNA knockdown of Bim/Puma, Western blot, subcellular fractionation, Co-IP Oncogene Medium 18794804
2009 Crystal structure of the human 9-1-1 complex determined at 3.0–3.2 Å resolution reveals a toroidal PCNA-like heterotrimeric ring. Unique interdomain connecting loops (IDC loops) of each subunit diverge from PCNA and confer repair-enzyme–specific activity; a co-crystal with FEN1 PIP-box peptide shows it binds to the IDC loop of Rad1. A single repair enzyme-binding site on 9-1-1 is competitively blocked by p21. X-ray crystallography, co-crystallization with FEN1 PIP-box peptide, competition binding biochemistry Molecular cell / The Journal of biological chemistry High 19446481 19535328
2009 Crystal structure of human 9(1-272)-1-1 at 2.5 Å; the complex forms a closed ring. The C-terminal tail of Rad9 inhibits stable complex binding to 5'-recessed DNA, as the Rad9(1-272)-1-1 complex but not full-length 9-1-1 forms a stable complex with 5'-recessed DNA. X-ray crystallography, electrophoretic mobility shift assay for DNA binding Journal of molecular biology High 19464297
2009 The 9-1-1 complex interacts with and stimulates hOGG1 (8-oxoguanine glycosylase) activity; individual subunits hRad9, hRad1, and hHus1 each enhance 8-oxoG excision and beta-elimination activities. Overexpression of all three 9-1-1 subunits with hOGG1 gives the greatest reduction of 8-oxoG in H2O2-treated cells. Co-immunoprecipitation, GST pulldown, in vitro glycosylase activity assay, flow cytometry for 8-oxoG DNA repair High 19615952
2010 Rad17 mediates the interaction of 9-1-1 with TopBP1 in Xenopus egg extracts. ATP binding to Rad17 is essential for 9-1-1/TopBP1 association; ATP hydrolysis by Rad17 is required for 9-1-1 loading onto DNA and checkpoint-dependent TopBP1 chromatin accumulation. A 9-1-1 mutant unable to bind TopBP1 still promotes TopBP1 chromatin accumulation. Xenopus egg extract immunodepletion, Rad17 ATPase mutants, chromatin fractionation Molecular biology of the cell High 20110345
2010 CK2 phosphorylates Ser-341 and Ser-387 in the Rad9 C-terminal tail; phosphorylation at these sites mediates interaction of 9-1-1 with TopBP1 in vitro, and phospho-deficient Rad9 mutant causes hypersensitivity to UV and MMS in cells. In vitro CK2 kinase assay, phosphomutant analysis, Co-immunoprecipitation, clonogenic survival Genes to cells High 20545769
2010 ATR phosphorylates Rad1 at T5 and Hus1 at S219/T223 in a TopBP1-dependent manner in Xenopus egg extracts. These phosphorylations are independent of Claspin and the Rad9 C-terminus (both required for Chk1 phosphorylation), defining an alternative ATR signaling readout. Xenopus egg extract immunodepletion and phosphomutant analysis, Western blot for phosphorylation Molecular biology of the cell High 16436514
2010 Each subunit of the human 9-1-1 complex interacts with hMSH2, hMSH3, and hMSH6. The 9-1-1 complex stimulates hMutSα DNA binding to G/T-containing substrates. Rad9 promotes MSH6 nuclear localization; in Rad9-knockdown cells, MSH6 is cytoplasmic and redistributed around the nuclear envelope after MNNG treatment. Co-immunoprecipitation, GST pulldown, in vitro DNA binding assay (EMSA), siRNA, immunofluorescence DNA repair Medium 20188637
2010 Crystal structure of eukaryotic MYH fragment reveals the interdomain connector (IDC, residues 295–350 of hMYH) adopts a stabilized conformation projecting from the catalytic domain to form a docking scaffold for 9-1-1. Disruption of the MYH/9-1-1 interaction via IDC mutations diminishes repair of oxidative DNA damage in vivo. X-ray crystallography of hMYH fragment, in vitro mutagenesis and interaction assay, in vivo mutation assay in S. pombe Journal of molecular biology High 20816984
2011 WRN helicase physically interacts with the 9-1-1 complex; this interaction is mediated by binding of the RAD1 subunit to the N-terminal region of WRN and is required for WRN relocalization to nuclear foci and ATR-dependent WRN phosphorylation in response to replication arrest. TopBP1 recruitment by 9-1-1 is required for ATR-dependent WRN phosphorylation. Co-immunoprecipitation with deletion mapping, immunofluorescence, siRNA knockdown, Western blot for phosphorylation Oncogene Medium 22002307
2012 EM reconstruction of the human 9-1-1/FEN1/DNA ternary complex at 18 Å reveals key differences from PCNA/FEN1/DNA in orientation and interactions, consistent with a more stable complex for DNA repair versus the flexible PCNA-FEN1 complex for lagging-strand replication. Single-particle electron microscopy, molecular dynamics simulations, clustering analysis Proceedings of the National Academy of Sciences of the United States of America Medium 22586102
2013 Conditional deletion of Hus1 in mouse testicular germ cells causes persistent unrepaired meiotic DSBs (γH2AX, RAD51 foci), synapsis defects, expanded XY body domain, and structural chromosome abnormalities. RAD9 localizes to RAD51-containing foci on meiotic chromosomes in a Hus1-dependent manner, while RAD1 and TOPBP1 localize to the XY body and unsynapsed autosomes independently of Hus1. Conditional KO by Cre-lox, meiotic chromosome spreads, immunofluorescence for γH2AX/RAD51/RAD9/RAD1/TOPBP1 PLoS genetics High 23468651
2014 The 9-1-1/TopBP1 interaction (via Rad9 CK2 phosphosites Ser-341/387) activates ATR-ATRIP and promotes TopBP1 recruitment to UV damage sites. UV promotes independent Rad9 chromatin loading (facilitated by RPA and Rad17); TopBP1/9-1-1 direct interaction then amplifies TopBP1 accumulation through ATR activation in a positive feedback loop. siRNA, phosphomutant Rad9, laser microirradiation, live cell imaging, chromatin fractionation DNA repair High 25091155
2015 Structure-function analysis of HUS1 identified: (1) a HUS1-RAD9A interface residue critical for 9-1-1 assembly and DNA loading; (2) positively charged inner-ring residues crucial for genotoxin-induced chromatin localization and ATR signaling; (3) two hydrophobic pockets on the HUS1 outer surface required for cell survival after DNA damage and for interaction with MYH, but not for chromatin localization or Chk1 phosphorylation. Site-directed mutagenesis, chromatin fractionation, Co-IP, clonogenic survival assay, Western blot for Chk1 phosphorylation The Journal of biological chemistry High 25911100
2015 Hus1 IDC loop residues (134–155) are key determinants of MYH binding. The N-terminal half of Hus1 (residues 1–146) binds DNA with moderate affinity, while the C-terminal half does not. Hus1(K136A) retains MYH binding but cannot stimulate MYH glycosylase activity. The 9-1-1 complex (with truncated Rad9) preferentially recruits to 5'-recessed DNA substrates in a complex-formation-dependent manner. GST pulldown with Hus1 deletion mutants, site-directed mutagenesis, in vitro glycosylase assay, EMSA DNA repair High 26021743
2015 SIRT6 interacts with and stimulates MYH glycosylase and APE1, and also interacts with the 9-1-1 checkpoint clamp; these interactions are enhanced by oxidative stress. SIRT6, APE1, and Hus1 bind overlapping but distinct sequence motifs on MYH and do not compete with each other, instead cooperatively enhancing each other's association with MYH. Hus1 recruitment to oxidatively damaged telomeres is partially dependent on SIRT6. Co-immunoprecipitation, GST pulldown, in vitro glycosylase assay, laser microirradiation on telomeres, KO cell imaging BMC molecular biology Medium 26063178
2015 The Rad9 C-terminal tail undergoes intramolecular binding to the core ring structure (CRS) of 9-1-1, specifically via a 15-aa stretch containing two conserved phenylalanines. This intramolecular binding prevents DNA association by the CRS. TopBP1 and CRS compete for binding to the same region of the Rad9 C-tail, suggesting competitive regulation of checkpoint activation and DNA binding. Deletion and point mutagenesis, in vitro DNA binding assay, purified protein competition binding assay The Journal of biological chemistry Medium 26088138
2018 FEN1 undergoes SUMO-1 modification in response to DNA replication fork-stalling agents (UV, hydroxyurea, mitomycin C). This SUMOylation promotes FEN1 interaction with the 9-1-1 complex (specifically with HUS1), enabling a switch from PCNA-dependent replication functions to 9-1-1-dependent DNA repair. FEN1 mutations blocking SUMOylation impair HUS1 interaction and stalled fork rescue. In vivo SUMOylation assay, Co-immunoprecipitation, FEN1 mutant cell complementation, DNA damage sensitivity assays Journal of molecular cell biology High 30184152
2019 Crystal structure of the 9-1-1 complex bound to a RHINO peptide reveals that RHINO binds unexpectedly to the edge and back of the 9-1-1 ring through specific interactions with the RAD1 subunit, demonstrating that 9-1-1 is a functionally double-faced DNA clamp. X-ray crystallography of 9-1-1 bound to RHINO peptide The Journal of biological chemistry High 31776186
2024 In Xenopus egg extracts, MRN and 9-1-1 act redundantly to stimulate Dna2-dependent long-range DSB end resection and ATR activation. 9-1-1 is dispensable for bulk Dna2 loading but is required for checkpoint-dependent TopBP1 loading. ATR facilitates Mre11 phosphorylation and ATM dissociation. Xenopus egg extract with defined DNA substrates, immunodepletion, phosphorylation analysis Nucleic acids research High 38349040
2025 The 9-1-1 complex (RAD9A-HUS1-RAD1) is essential for survival of BRCA2-deficient cells through an ATR-independent mechanism. Loss of 9-1-1 in BRCA2-deficient cells causes accumulation of PRIMPOL-dependent ssDNA gaps that undergo excessive EXO1-mediated degradation and fail to undergo post-replicative repair. EXO1 depletion rescues this phenotype. 9-1-1 is required for POLζ-dependent gap filling. Genome-wide CRISPR screen, genetic epistasis (EXO1 and PRIMPOL depletion), ssDNA gap assay bioRxivpreprint Medium bio_10.1101_2025.10.07.680950

Source papers

Stage 0 corpus · 90 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 The Rad9-Hus1-Rad1 (9-1-1) clamp activates checkpoint signaling via TopBP1. Genes & development 388 17575048
2004 Dial 9-1-1 for DNA damage: the Rad9-Hus1-Rad1 (9-1-1) clamp complex. DNA repair 257 15279787
2007 The Rad9-Hus1-Rad1 checkpoint clamp regulates interaction of TopBP1 with ATR. The Journal of biological chemistry 232 17636252
2002 Caenorhabditis elegans HUS-1 is a DNA damage checkpoint protein required for genome stability and EGL-1-mediated apoptosis. Current biology : CB 226 12445383
2000 Structure-based predictions of Rad1, Rad9, Hus1 and Rad17 participation in sliding clamp and clamp-loading complexes. Nucleic acids research 217 10871397
2000 Characterization of Schizosaccharomyces pombe Hus1: a PCNA-related protein that associates with Rad1 and Rad9. Molecular and cellular biology 202 10648611
1999 Human homologs of Schizosaccharomyces pombe rad1, hus1, and rad9 form a DNA damage-responsive protein complex. The Journal of biological chemistry 168 9872989
2004 Human immunodeficiency virus type 1 Vpr-mediated G2 arrest requires Rad17 and Hus1 and induces nuclear BRCA1 and gamma-H2AX focus formation. Molecular and cellular biology 114 15485898
2000 Inactivation of mouse Hus1 results in genomic instability and impaired responses to genotoxic stress. Genes & development 106 10921903
2004 The human Rad9/Rad1/Hus1 damage sensor clamp interacts with DNA polymerase beta and increases its DNA substrate utilisation efficiency: implications for DNA repair. Nucleic acids research 103 15314187
2009 Crystal structure of the rad9-rad1-hus1 DNA damage checkpoint complex--implications for clamp loading and regulation. Molecular cell 102 19446481
2004 ATR, Claspin and the Rad9-Rad1-Hus1 complex regulate Chk1 and Cdc25A in the absence of DNA damage. Cell cycle (Georgetown, Tex.) 101 15190204
2002 The role of single-stranded DNA and polymerase alpha in establishing the ATR, Hus1 DNA replication checkpoint. The Journal of biological chemistry 100 12015327
2005 Interaction and colocalization of Rad9/Rad1/Hus1 checkpoint complex with replication protein A in human cells. Oncogene 93 15897895
2004 The human Rad9-Rad1-Hus1 checkpoint complex stimulates flap endonuclease 1. Proceedings of the National Academy of Sciences of the United States of America 88 15556996
2006 Physical and functional interactions between MutY glycosylase homologue (MYH) and checkpoint proteins Rad9-Rad1-Hus1. The Biochemical journal 82 16879101
2002 Hus1 acts upstream of chk1 in a mammalian DNA damage response pathway. Current biology : CB 77 11790307
2009 Structure and functional implications of the human rad9-hus1-rad1 cell cycle checkpoint complex. The Journal of biological chemistry 71 19535328
2004 Interaction of checkpoint proteins Hus1/Rad1/Rad9 with DNA base excision repair enzyme MutY homolog in fission yeast, Schizosaccharomyces pombe. The Journal of biological chemistry 70 15533944
2002 Genotoxin-induced Rad9-Hus1-Rad1 (9-1-1) chromatin association is an early checkpoint signaling event. The Journal of biological chemistry 66 12228248
2007 The human checkpoint sensor Rad9-Rad1-Hus1 interacts with and stimulates NEIL1 glycosylase. Nucleic acids research 65 17395641
2009 Crystal structure of the human rad9-hus1-rad1 clamp. Journal of molecular biology 63 19464297
2003 Critical role for mouse Hus1 in an S-phase DNA damage cell cycle checkpoint. Molecular and cellular biology 62 12529385
2007 The checkpoint clamp, Rad9-Rad1-Hus1 complex, preferentially stimulates the activity of apurinic/apyrimidinic endonuclease 1 and DNA polymerase beta in long patch base excision repair. Nucleic acids research 61 17426133
2005 The human checkpoint sensor and alternative DNA clamp Rad9-Rad1-Hus1 modulates the activity of DNA ligase I, a component of the long-patch base excision repair machinery. The Biochemical journal 60 15871698
2005 The two DNA clamps Rad9/Rad1/Hus1 complex and proliferating cell nuclear antigen differentially regulate flap endonuclease 1 activity. Journal of molecular biology 60 16216273
2004 Disruption of the Rad9/Rad1/Hus1 (9-1-1) complex leads to checkpoint signaling and replication defects. Oncogene 59 15184880
2000 HDAC1, a histone deacetylase, forms a complex with Hus1 and Rad9, two G2/M checkpoint Rad proteins. The Journal of biological chemistry 59 10846170
2010 Rad17 plays a central role in establishment of the interaction between TopBP1 and the Rad9-Hus1-Rad1 complex at stalled replication forks. Molecular biology of the cell 57 20110345
2010 A structural hinge in eukaryotic MutY homologues mediates catalytic activity and Rad9-Rad1-Hus1 checkpoint complex interactions. Journal of molecular biology 55 20816984
2007 The human checkpoint sensor Rad9-Rad1-Hus1 interacts with and stimulates DNA repair enzyme TDG glycosylase. Nucleic acids research 55 17855402
2013 Conditional inactivation of the DNA damage response gene Hus1 in mouse testis reveals separable roles for components of the RAD9-RAD1-HUS1 complex in meiotic chromosome maintenance. PLoS genetics 50 23468651
2007 Cadmium-induced germline apoptosis in Caenorhabditis elegans: the roles of HUS1, p53, and MAPK signaling pathways. Toxicological sciences : an official journal of the Society of Toxicology 50 17728284
2012 Repair complexes of FEN1 endonuclease, DNA, and Rad9-Hus1-Rad1 are distinguished from their PCNA counterparts by functionally important stability. Proceedings of the National Academy of Sciences of the United States of America 48 22586102
2006 Mechanism of stimulation of human DNA ligase I by the Rad9-rad1-Hus1 checkpoint complex. The Journal of biological chemistry 45 16731526
2006 Telomere and telomerase modulation by the mammalian Rad9/Rad1/Hus1 DNA-damage-checkpoint complex. Current biology : CB 44 16890531
1998 cDNA cloning and gene mapping of human homologs for Schizosaccharomyces pombe rad17, rad1, and hus1 and cloning of homologs from mouse, Caenorhabditis elegans, and Drosophila melanogaster. Genomics 43 9878245
2015 SIRT6 protein deacetylase interacts with MYH DNA glycosylase, APE1 endonuclease, and Rad9-Rad1-Hus1 checkpoint clamp. BMC molecular biology 41 26063178
2001 Structure-function analysis of fission yeast Hus1-Rad1-Rad9 checkpoint complex. Molecular biology of the cell 40 11739777
1997 Molecular analysis of hus1+, a fission yeast gene required for S-M and DNA damage checkpoints. Molecular & general genetics : MGG 40 9180692
2010 Casein kinase 2-dependent phosphorylation of human Rad9 mediates the interaction between human Rad9-Hus1-Rad1 complex and TopBP1. Genes to cells : devoted to molecular & cellular mechanisms 38 20545769
2014 Interaction between Rad9-Hus1-Rad1 and TopBP1 activates ATR-ATRIP and promotes TopBP1 recruitment to sites of UV-damage. DNA repair 33 25091155
2007 Increased common fragile site expression, cell proliferation defects, and apoptosis following conditional inactivation of mouse Hus1 in primary cultured cells. Molecular biology of the cell 31 17215515
2006 Phosphorylation of Xenopus Rad1 and Hus1 defines a readout for ATR activation that is independent of Claspin and the Rad9 carboxy terminus. Molecular biology of the cell 30 16436514
2015 Distinct functional consequences of MUTYH variants associated with colorectal cancer: Damaged DNA affinity, glycosylase activity and interaction with PCNA and Hus1. DNA repair 28 26377631
2002 Identification and characterization of a paralog of human cell cycle checkpoint gene HUS1. Genomics 28 11944979
2016 Functional compartmentalization of Rad9 and Hus1 reveals diverse assembly of the 9-1-1 complex components during the DNA damage response in Leishmania. Molecular microbiology 27 27301589
2007 Jab1 mediates protein degradation of the Rad9-Rad1-Hus1 checkpoint complex. Journal of molecular biology 27 17583730
2009 Repair activities of human 8-oxoguanine DNA glycosylase are stimulated by the interaction with human checkpoint sensor Rad9-Rad1-Hus1 complex. DNA repair 26 19615952
2004 Involvement of Hus1 in the chain elongation step of DNA replication after exposure to camptothecin or ionizing radiation. Nucleic acids research 26 14762204
2011 The RAD9-RAD1-HUS1 (9.1.1) complex interacts with WRN and is crucial to regulate its response to replication fork stalling. Oncogene 25 22002307
2018 Conditional genome engineering reveals canonical and divergent roles for the Hus1 component of the 9-1-1 complex in the maintenance of the plastic genome of Leishmania. Nucleic acids research 23 30380080
2013 Expression of cell cycle regulatory factors hus1, gadd45a, rb1, cdkn2a and mre11a correlates with expression of clock gene per2 in human colorectal carcinoma tissue. Molecular biology reports 23 24062075
2006 The effect of Hus1 on ionizing radiation sensitivity is associated with homologous recombination repair but is independent of nonhomologous end-joining. Oncogene 23 16278671
2007 An essential role for Drosophila hus1 in somatic and meiotic DNA damage responses. Journal of cell science 21 17327271
2009 The Drosophila hus1 gene is required for homologous recombination repair during meiosis. Mechanisms of development 20 19501158
2010 Interaction between human mismatch repair recognition proteins and checkpoint sensor Rad9-Rad1-Hus1. DNA repair 19 20188637
2005 Conditional inactivation of the mouse Hus1 cell cycle checkpoint gene. Genomics 18 15919177
2018 SUMO-1 modification of FEN1 facilitates its interaction with Rad9-Rad1-Hus1 to counteract DNA replication stress. Journal of molecular cell biology 17 30184152
2015 Genome Protection by the 9-1-1 Complex Subunit HUS1 Requires Clamp Formation, DNA Contacts, and ATR Signaling-independent Effector Functions. The Journal of biological chemistry 17 25911100
2015 Association of the Rad9-Rad1-Hus1 checkpoint clamp with MYH DNA glycosylase and DNA. DNA repair 16 26021743
2011 Synthesis and crystal structure of a layered silicate HUS-1 with a halved sodalite-cage topology. Inorganic chemistry 16 21294579
2007 Genome maintenance defects in cultured cells and mice following partial inactivation of the essential cell cycle checkpoint gene Hus1. Molecular and cellular biology 16 17220276
2002 Downregulation of Hus1 by antisense oligonucleotides enhances the sensitivity of human lung carcinoma cells to cisplatin. Cancer 16 11920544
2012 Disease severity in a mouse model of ataxia telangiectasia is modulated by the DNA damage checkpoint gene Hus1. Human molecular genetics 14 22575700
1999 Mouse Hus1, a homolog of the Schizosaccharomyces pombe hus1+ cell cycle checkpoint gene. Genomics 14 10395797
1999 Phytochrome-induced expression of lig1, a homologue of the fission yeast cell-cycle checkpoint gene hus1, is associated with the developmental switch in Physarum polycephalum plasmodia. Current genetics 14 10447599
2011 The Hus1 homologue of Leishmania major encodes a nuclear protein that participates in DNA damage response. Molecular and biochemical parasitology 13 21291918
2009 Dual inactivation of Hus1 and p53 in the mouse mammary gland results in accumulation of damaged cells and impaired tissue regeneration. Proceedings of the National Academy of Sciences of the United States of America 13 19918068
2022 The Rad9-Rad1-Hus1 DNA Repair Clamp is Found in Microsporidia. Genome biology and evolution 12 35439302
2020 An ordered assembly of MYH glycosylase, SIRT6 protein deacetylase, and Rad9-Rad1-Hus1 checkpoint clamp at oxidatively damaged telomeres. Aging 11 32991318
2015 Intramolecular Binding of the Rad9 C Terminus in the Checkpoint Clamp Rad9-Hus1-Rad1 Is Closely Linked with Its DNA Binding. The Journal of biological chemistry 11 26088138
2013 Opening pathways of the DNA clamps proliferating cell nuclear antigen and Rad9-Rad1-Hus1. Nucleic acids research 10 24038358
2008 Loss of Hus1 sensitizes cells to etoposide-induced apoptosis by regulating BH3-only proteins. Oncogene 10 18794804
2019 Structure of the RAD9-RAD1-HUS1 checkpoint clamp bound to RHINO sheds light on the other side of the DNA clamp. The Journal of biological chemistry 9 31776186
2018 HUS1 checkpoint clamp component (HUS1) is a potential tumor suppressor in primary hepatocellular carcinoma. Molecular carcinogenesis 9 30182378
2015 HUS1 regulates in vivo responses to genotoxic chemotherapies. Oncogene 9 25915840
2022 DNA binding by the Rad9A subunit of the Rad9-Rad1-Hus1 complex. PloS one 8 35939452
2010 Roles of the checkpoint sensor clamp Rad9-Rad1-Hus1 (911)-complex and the clamp loaders Rad17-RFC and Ctf18-RFC in Schizosaccharomyces pombe telomere maintenance. Cell cycle (Georgetown, Tex.) 8 20505337
2021 MiR-340-3p-HUS1 axis suppresses proliferation and migration in lung adenocarcinoma cells. Life sciences 6 33711383
2015 The Roles of p21(Waf1/CIP1) and Hus1 in Generation and Transmission of Damage Signals Stimulated by Low-Dose Alpha-Particle Irradiation. Radiation research 6 26600172
2011 Toxicity of carbon nanotubes to p21 and hus1 gene deficient mammalian cells. Journal of nanoscience and nanotechnology 6 22409043
2024 Resection of DNA double-strand breaks activates Mre11-Rad50-Nbs1- and Rad9-Hus1-Rad1-dependent mechanisms that redundantly promote ATR checkpoint activation and end processing in Xenopus egg extracts. Nucleic acids research 5 38349040
2007 Tri-cistronic cloning, overexpression and purification of human Rad9, Rad1, Hus1 protein complex. Protein expression and purification 4 17493829
2022 Structural basis for molecular interactions on the eukaryotic DNA sliding clamps PCNA and RAD9-RAD1-HUS1. Journal of biochemistry 3 35731009
2015 The effect of ionizing radiation on mRNA levels of the DNA damage response genes rad9, rad1 and hus1 in various mouse tissues. Radiation research 3 25564717
2014 Identification of a candidate rad1 subunit for the kinetoplastid 9-1-1 (rad9-hus1-rad1) complex. Biology 3 25534152
2023 Using Affinity Pulldown Assays to Study Protein-Protein Interactions of Human NEIL1 Glycosylase and the Checkpoint Protein RAD9-RAD1-HUS1 (9-1-1) Complex. Methods in molecular biology (Clifton, N.J.) 2 37574484
2022 HUS1 as a Potential Therapeutic Target in Urothelial Cancer. Journal of clinical medicine 2 35456300
2026 Energetically equivalent structural transitions in the Rad17-Rad9-Hus1-Rad1-Rhino complex underlie the sequential progression from activation through maintenance to inactivation of the ATR-dependent DNA damage response. Nucleic acids research 0 41693569

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