Affinage

HUS1

Checkpoint protein HUS1 · UniProt O60921

Length
280 aa
Mass
31.7 kDa
Annotated
2026-04-28
90 papers in source corpus 49 papers cited in narrative 49 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HUS1 is a core subunit of the heterotrimeric RAD9-HUS1-RAD1 (9-1-1) sliding clamp, a PCNA-like toroidal ring that is loaded onto damaged DNA by the RAD17-RFC clamp loader and serves as a central platform for both DNA damage checkpoint signaling and base excision repair. In checkpoint signaling, the 9-1-1 complex recruits TopBP1 via CK2-phosphorylated Ser-341/Ser-387 residues on the Rad9 C-terminal tail, thereby stimulating ATR-mediated CHK1 phosphorylation; HUS1 itself is phosphorylated by ATR at Ser-219 and Thr-223 (PMID:17575048, PMID:20545769, PMID:16436514). In DNA repair, the 9-1-1 complex directly binds and stimulates multiple BER enzymes—including DNA polymerase β, FEN1, DNA ligase I, APE1, MYH, NEIL1, TDG, and OGG1—with HUS1 contributing specific protein-interaction surfaces (interdomain connecting loop residues 134–155 for MYH) and an N-terminal DNA-binding domain that are functionally separable from its checkpoint role (PMID:15314187, PMID:15556996, PMID:18794804, PMID:25911100, PMID:26021743). Hus1 loss in mice causes embryonic lethality, spontaneous chromosomal breaks at common fragile sites, telomere shortening, and meiotic DSB repair defects, underscoring its essential role in genome maintenance across multiple cellular contexts (PMID:10921903, PMID:17215515, PMID:23468651).

Mechanistic history

Synthesis pass · year-by-year structured walk · 17 steps
  1. 1999 High

    Establishing HUS1 as part of a conserved heterotrimeric checkpoint complex resolved how three PCNA-related proteins cooperate in the DNA damage response.

    Evidence Reciprocal co-immunoprecipitation from human cells showed HUS1 forms a stable complex with RAD9 and RAD1, with RAD9 phosphorylation upon DNA damage.

    PMID:9872989

    Open questions at the time
    • Stoichiometry and architecture of the complex unknown
    • How the complex is loaded onto DNA not addressed
    • Functional consequence of RAD9 phosphorylation unclear
  2. 2000 Medium

    Computational modeling predicted the 9-1-1 ring adopts a PCNA-like toroidal fold with a defined Rad1-Hus1-Rad9 subunit order, framing the complex as a damage-specific sliding clamp.

    Evidence Fold recognition and comparative modeling predicted PCNA-like domains for each subunit.

    PMID:10871397

    Open questions at the time
    • No experimental structure yet
    • Ring opening/loading mechanism unknown
    • DNA binding mode not established
  3. 2000 High

    Genetic knockout established that HUS1 is essential for embryonic viability, genomic stability, and selective genotoxic stress responses, distinguishing the 9-1-1 pathway from ATM-dependent IR responses.

    Evidence Hus1 knockout mice showed mid-gestational lethality, spontaneous chromosomal abnormalities, and UV/HU hypersensitivity with only slight IR sensitivity.

    PMID:10921903

    Open questions at the time
    • Downstream signaling targets not identified
    • Whether checkpoint and repair functions are separable unknown
    • Mechanism of selective UV/HU sensitivity unclear
  4. 2002 High

    Epistasis experiments placed HUS1 upstream of CHK1 phosphorylation but not CHK2 or p53, defining HUS1 as a specific activator of the ATR-CHK1 axis.

    Evidence Hus1-null MEFs showed greatly reduced genotoxin-induced CHK1 phosphorylation rescued by retroviral Hus1 re-expression; CHK2 and p53 were unaffected.

    PMID:11790307

    Open questions at the time
    • How 9-1-1 activates ATR not mechanistically resolved
    • Whether 9-1-1 chromatin loading requires DNA replication debated
    • Identity of intermediate adaptor between 9-1-1 and ATR unknown
  5. 2002 High

    Chromatin loading studies revealed that 9-1-1 associates with damaged DNA independently of ATM/ATR/DNA-PK kinase activity, establishing it as a proximal damage sensor rather than a downstream effector.

    Evidence Genotoxin-induced 9-1-1 chromatin binding persisted in the presence of PIKK inhibitors and without DNA replication; Xenopus studies showed RPA-dependent but pol-α-independent loading.

    PMID:12015327 PMID:12228248

    Open questions at the time
    • Structural basis for clamp loading not resolved
    • Whether loading requires 5'-recessed junctions in vivo unknown
    • Rad17-RFC clamp loader mechanism not biochemically dissected
  6. 2004 High

    Biochemical reconstitution revealed that 9-1-1 directly binds and stimulates multiple BER enzymes (Pol β, FEN1, MYH), establishing it as a damage-specific repair scaffold analogous to PCNA's role in replication.

    Evidence Purified 9-1-1 enhanced Pol β primer-template affinity and strand displacement, stimulated FEN1 on flap/nick/gap substrates, and enhanced MYH glycosylase activity via HUS1-specific binding.

    PMID:15314187 PMID:15533944 PMID:15556996

    Open questions at the time
    • Whether 9-1-1 must encircle DNA to stimulate repair enzymes debated
    • Relative contributions of individual subunits to each repair enzyme not mapped
    • In vivo relevance of repair stimulation not yet demonstrated genetically
  7. 2005 High

    Extension of the BER scaffold model showed 9-1-1 also stimulates DNA ligase I and that acetylation of FEN1 selectively abolishes 9-1-1 but not PCNA stimulation, revealing post-translational regulation of the 9-1-1/repair interface.

    Evidence 9-1-1 enhanced ligase I binding to nicked DNA; p300-mediated FEN1 acetylation blocked 9-1-1-dependent but not PCNA-dependent FEN1 stimulation.

    PMID:15871698 PMID:16216273

    Open questions at the time
    • Physiological conditions triggering FEN1 acetylation switch unclear
    • Whether all BER enzymes share a common 9-1-1 binding site unknown
  8. 2007 High

    The mechanism of ATR activation was resolved: 9-1-1 recruits TopBP1 via phosphorylated Rad9 C-terminal Ser-373, and TopBP1's ATR-activation domain then stimulates ATR kinase activity—a function bypassable by fusing the AD to PCNA or histones.

    Evidence Xenopus egg extract experiments with Rad9 S373A mutants, TopBP1 dominant-negative fragments, and AD-PCNA/H2B fusions demonstrated that 9-1-1 serves as a localization platform for TopBP1.

    PMID:17575048 PMID:17636252

    Open questions at the time
    • How TopBP1 binding is regulated temporally at damage sites not established
    • Whether 9-1-1-independent TopBP1 recruitment pathways exist in mammals unclear
  9. 2007 High

    The BER scaffold role was extended to additional glycosylases (NEIL1, TDG, OGG1) and APE1, and reconstituted long-patch BER showed 9-1-1 enhances the entire early repair pathway.

    Evidence In vitro reconstitution showed 9-1-1 stimulated NEIL1, TDG, OGG1 glycosylase activities and APE1 endonuclease; complete LP-BER was enhanced by 9-1-1.

    PMID:17395641 PMID:17426133 PMID:17855402

    Open questions at the time
    • Whether 9-1-1 coordinates sequential handoff between BER enzymes unknown
    • Structural basis for glycosylase binding not resolved at atomic level
  10. 2007 High

    Hus1 loss causes spontaneous chromosomal breaks preferentially at common fragile sites, revealing a replication stress protection function independent of p53.

    Evidence Conditional Hus1 knockout fibroblasts accumulated γH2AX and breaks at fragile sites; p53 co-deletion did not rescue proliferation or reduce apoptosis.

    PMID:17215515

    Open questions at the time
    • Whether fragile site instability reflects checkpoint failure, repair deficiency, or both unknown
    • Mechanism of replication fork stabilization by 9-1-1 at fragile sites not dissected
  11. 2009 High

    Crystal structures of the human 9-1-1 complex confirmed the PCNA-like toroidal architecture, revealed asymmetric subunit interfaces, and showed that the Rad9 C-terminal tail autoinhibits DNA binding.

    Evidence Two independent X-ray structures (2.5–3.2 Å) showed the closed ring; deletion of Rad9 C-tail enabled stable DNA binding; a single repair enzyme-binding site was competitively blocked by p21.

    PMID:19446481 PMID:19464297

    Open questions at the time
    • No structure of 9-1-1 loaded on DNA available
    • How the ring opens for loading not structurally resolved
    • Structural basis for individual subunit–enzyme contacts incomplete
  12. 2010 High

    CK2 was identified as the kinase phosphorylating Rad9 Ser-341/Ser-387, establishing the molecular switch that enables TopBP1 recruitment and ATR activation; separately, Rad17 ATP binding and hydrolysis were shown to drive sequential 9-1-1 loading and TopBP1 accumulation.

    Evidence In vitro kinase assays with CK2, mutagenesis of Ser-341/387, and Rad17 ATPase mutants in Xenopus extracts dissected the loading-to-signaling transition.

    PMID:20110345 PMID:20545769

    Open questions at the time
    • How CK2 access to Rad9 C-tail is regulated spatiotemporally unclear
    • Whether Rad17 remains associated after loading not resolved
  13. 2013 High

    Conditional Hus1 deletion in male germ cells revealed an essential meiotic function: 9-1-1 is required for meiotic DSB repair and synapsis, with HUS1-dependent RAD9 localization to RAD51 foci distinguishable from HUS1-independent RAD1/TOPBP1 localization.

    Evidence Conditional testis knockout showed persistent γH2AX, RAD51 foci, synapsis defects, and chromosome abnormalities in spermatocytes.

    PMID:23468651

    Open questions at the time
    • Whether 9-1-1 directly promotes strand invasion or only signals checkpoint arrest during meiosis unknown
    • Mechanism of HUS1-dependent RAD9 localization to meiotic DSBs not resolved
  14. 2015 High

    Structure-function dissection of HUS1 separated three functional surfaces: positively charged inner-ring residues for DNA binding and ATR signaling, two hydrophobic outer-surface pockets for repair enzyme binding (e.g., MYH), and the interdomain connecting loop (residues 134–155) as the primary MYH-binding determinant.

    Evidence Systematic mutagenesis with genotoxin sensitivity, CHK1 phosphorylation, MYH binding, and glycosylase stimulation assays.

    PMID:25911100 PMID:26021743

    Open questions at the time
    • Atomic-resolution structure of HUS1-MYH interface not available
    • Whether other repair enzymes use the same hydrophobic pockets unknown
    • How DNA binding by HUS1 N-terminal domain contributes to repair stimulation unclear
  15. 2015 High

    An autoinhibition mechanism was elucidated: the Rad9 C-tail intramolecularly binds the 9-1-1 core ring via two consecutive phenylalanines, blocking DNA binding; TopBP1 competes for this same motif, coupling TopBP1 recruitment to relief of autoinhibition.

    Evidence Purified protein binding assays with deletion mutants and competitive TopBP1 binding.

    PMID:26088138

    Open questions at the time
    • Whether autoinhibition relief occurs before or after DNA loading in vivo unknown
    • Structural details of the tail–core interface not resolved at atomic level
  16. 2018 High

    SUMO-1 modification of FEN1 was identified as a molecular switch directing FEN1 from PCNA to HUS1/9-1-1 at stalled replication forks, linking post-translational modification to partner selection during replication stress.

    Evidence SUMOylation assays, co-IP showing SUMO-FEN1 preferentially binds HUS1, and fork restart assays with SUMO-site FEN1 mutants.

    PMID:30184152

    Open questions at the time
    • E3 SUMO ligase responsible for FEN1 SUMOylation at forks not identified
    • Whether similar SUMO switches operate for other 9-1-1 repair partners unknown
  17. 2024 High

    9-1-1 was found to redundantly stimulate Dna2-dependent long-range DSB end resection together with MRN, and to be interdependent with TopBP1 loading, extending 9-1-1 function beyond checkpoint and BER into DSB resection.

    Evidence Xenopus egg extract immunodepletion of 9-1-1 and MRN with DNA substrate resection assays.

    PMID:38349040

    Open questions at the time
    • Whether 9-1-1 directly contacts Dna2 or acts indirectly via TopBP1/ATR unknown
    • Relative contribution of 9-1-1 vs MRN to resection in mammalian cells not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include how 9-1-1 coordinates sequential handoff between repair enzymes on the same DNA lesion, whether the checkpoint and repair functions of 9-1-1 are temporally separable at individual damage sites, and the structural basis for 9-1-1 ring opening and loading by Rad17-RFC.
  • No structure of Rad17-RFC loading 9-1-1 onto DNA
  • No single-molecule studies of 9-1-1 enzyme coordination
  • ATR-independent functions of 9-1-1 in BRCA2-deficient contexts await peer-reviewed validation

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 7 GO:0098772 molecular function regulator activity 5 GO:0003677 DNA binding 3 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0005694 chromosome 5 GO:0005634 nucleus 3
Pathway
R-HSA-73894 DNA Repair 13 R-HSA-162582 Signal Transduction 5 R-HSA-1640170 Cell Cycle 4 R-HSA-5357801 Programmed Cell Death 2
Partners
APE1FEN1LIG1MUTYHPOLBRAD1RAD9ATOPBP1
Complex memberships
RAD9-HUS1-RAD1 (9-1-1) clamp

Evidence

Reading pass · 49 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 is phosphorylated in response to DNA damage and is a key participant in complex formation. Co-immunoprecipitation from human cells The Journal of biological chemistry High 9872989
2000 Structure-based computational predictions established that Rad9, Hus1, and Rad1 each adopt a PCNA-like fold and form a heterotrimeric ring in the order Rad1-Hus1-Rad9, analogous to the PCNA sliding clamp. Fold recognition, comparative modeling, generalized sequence profiles Nucleic acids research Medium 10871397
2000 Fission yeast Hus1 associates with Rad9 and Rad1 in a stable complex; Hus1 nuclear localization depends on Rad17; Hus1 is phosphorylated after irradiation. Co-immunoprecipitation, cofractionation, indirect immunofluorescence, MYC-tag pulldown Molecular and cellular biology High 10648611
2000 Mouse Hus1 inactivation results in mid-gestational embryonic lethality, spontaneous chromosomal abnormalities in primary cells, and selective hypersensitivity to hydroxyurea and UV but only slight sensitivity to ionizing radiation, establishing Hus1 as required for genomic stability and genotoxic stress responses. Targeted gene disruption (knockout mouse), clonogenic assays, chromosomal analysis Genes & development High 10921903
2000 HDAC1 forms a complex with human HUS1 and RAD9 in mammalian cells and in vitro, linking the 9-1-1 complex to chromatin modification machinery. Yeast two-hybrid, co-immunoprecipitation from mammalian cells, in vitro binding The Journal of biological chemistry Medium 10846170
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 rescued by retroviral Hus1 re-expression, while Chk2 phosphorylation and p53 responses are intact. Genetic knockout, retroviral complementation, Western blot for phosphorylated Chk1/Chk2 Current biology : CB High 11790307
2002 Xenopus Hus1 (Xhus1) associates with chromatin in a DNA replication initiation-dependent manner and is required for checkpoint-dependent Chk1 phosphorylation; its chromatin association requires RPA but not polymerase alpha, distinguishing it from ATR chromatin loading. Nucleus-free DNA replication system, chromatin fractionation, immunodepletion The Journal of biological chemistry High 12015327
2002 C. elegans HUS-1 relocalizes to chromatin foci following DNA damage, is required for DNA damage-induced cell cycle arrest, genome stability (prevents spontaneous mutations, chromosome nondisjunction, telomere shortening), and promotes EGL-1/BH3-only protein transcription via CEP-1/p53 to induce apoptosis. Loss-of-function genetics, immunofluorescence relocalization, mutation frequency assays, chromosome nondisjunction assays Current biology : CB High 12445383
2002 Genotoxin-induced 9-1-1 chromatin binding is a proximal checkpoint event that does not require ATM, ATR, or DNA-PK catalytic activity, and does not require DNA replication, indicating the complex can be loaded at non-replication fork DNA structures. Chromatin fractionation, PIKK inhibitors, DNA replication block, phospho-site mutants The Journal of biological chemistry High 12228248
2003 Hus1 is required specifically for the S-phase DNA damage checkpoint in response to bulky DNA adducts (BPDE) but not DNA strand break-inducing agents (ionizing radiation), identifying separable mammalian S-phase checkpoint pathways. Knockout MEFs, DNA synthesis measurement, checkpoint assays with different genotoxins Molecular and cellular biology High 12529385
2004 The 9-1-1 complex physically interacts with DNA polymerase beta in vitro and stimulates its activity by increasing affinity for the primer-template; 9-1-1 also enhances strand displacement synthesis by Pol beta but does not affect Pol lambda, Pol alpha, or Pol delta. In vitro pulldown, in vitro DNA polymerase activity assays Nucleic acids research High 15314187
2004 The 9-1-1 complex binds and stimulates FEN1 on flap, nick, and gapped DNA substrates; blocking 9-1-1 entry to double strands reduces stimulation; 9-1-1 does not substitute for PCNA in stimulating DNA polymerase beta, establishing 9-1-1 as a damage-specific FEN1 activator. In vitro binding and endonuclease activity assays with purified proteins Proceedings of the National Academy of Sciences of the United States of America High 15556996
2004 Fission yeast MYH physically interacts with all three subunits of the SpRad9/SpRad1/SpHus1 complex; SpHus1 binding site is distinct from the PCNA binding site on SpMYH; interaction increases after H2O2 treatment correlating with SpHus1 phosphorylation; SpHus1 and 9-1-1 enhance SpMYH glycosylase activity. Co-immunoprecipitation, bacterial expression pulldown, glycosylase activity assays The Journal of biological chemistry High 15533944
2004 Rad17 and Hus1 are required for HIV-1 Vpr-induced G2 arrest, which also requires ATR and produces nuclear γ-H2AX and BRCA1 foci, placing the 9-1-1 complex in the ATR pathway activated by Vpr. siRNA knockdown of Rad17 and Hus1, cell cycle analysis, immunofluorescence Molecular and cellular biology Medium 15485898
2004 Hus1 loss impairs the S-phase checkpoint and chain elongation step of DNA replication (not replicon initiation) following camptothecin or high-dose ionizing radiation, correlated with reduced PCNA dissociation from replication foci. Knockout MEFs, DNA replication assays, PCNA foci analysis Nucleic acids research Medium 14762204
2005 The 9-1-1 complex directly interacts with RPA (via Rad9 binding to RPA70 and RPA32 subunits) in human cells; UV or camptothecin stimulates this interaction and co-localization; RPA knockdown blocks damage-dependent 9-1-1 chromatin association and inhibits 9-1-1 complex formation. Co-immunoprecipitation, GST pulldown, siRNA, nuclear foci co-localization Oncogene High 15897895
2005 9-1-1 physically interacts with and stimulates DNA ligase I; the 9-1-1/ligase I complex can be immunoprecipitated from human cells; UV irradiation enhances this interaction; stimulation occurs on linear substrates indicating clamp encirclement is not required, unlike PCNA. Co-immunoprecipitation from human cells, in vitro ligation assays The Biochemical journal High 15871698
2005 PCNA and 9-1-1 independently bind and stimulate FEN1; acetylation of FEN1 by p300-HAT abolishes 9-1-1-mediated stimulation but not PCNA-mediated stimulation, revealing a regulatory mechanism specific to the 9-1-1/FEN1 interaction. In vitro binding, FEN1 activity assays, acetylation by p300 Journal of molecular biology High 16216273
2006 Human MYH interacts specifically with hHus1 and hRad1 (not hRad9); the Hus1-binding site maps to residues 295–350 of hMYH (Val315 critical); hHus1 and the S. pombe 9-1-1 complex enhance SpMYH glycosylase activity; interaction is enhanced by ionizing radiation. Co-immunoprecipitation, bacterial pulldown, mutagenesis, glycosylase activity assays The Biochemical journal High 16879101
2006 9-1-1 stimulates DNA ligase I by improving its binding to nicked double-stranded DNA; stimulation is specific for DNA ligase I and independent of casein kinase II inhibition of ligase I, suggesting a direct activation mechanism distinct from PCNA. In vitro ligation assays, DNA binding assays with purified proteins The Journal of biological chemistry High 16731526
2006 The mammalian 9-1-1 complex localizes to telomeres in human and mouse cells, and Hus1 deficiency causes severe telomere shortening; 9-1-1 is found in association with catalytically competent telomerase and positively regulates its DNA polymerase activity. Quantitative telomere length measurement, conditional knockout, co-IP with telomerase Current biology : CB Medium 16890531
2007 The 9-1-1 complex activates Chk1 by binding TopBP1 via the C-terminal domain of Rad9 (phospho-Ser-373/Ser-387); TopBP1's ATR-activation domain (AD) then stimulates ATR-mediated Chk1 phosphorylation; fusion of the AD to PCNA or histone H2B bypasses the requirement for 9-1-1. Co-IP, epistasis with AD-PCNA and AD-H2B fusions, Xenopus egg extract checkpoint assays, mutagenesis Genes & development High 17575048
2007 TopBP1 BRCT I-II repeats bind the 9-1-1 complex via the phosphorylated C-terminal domain of Rad9 (Ser-373); this interaction is required for checkpoint-stimulated binding of TopBP1 to ATR-ATRIP and subsequent ATR activation. Xenopus egg extract biochemistry, mutagenesis (Rad9 S373A), dominant-negative C-terminal Rad9 fragment inhibition The Journal of biological chemistry High 17636252
2007 The 9-1-1 complex physically interacts with and stimulates NEIL1 glycosylase; residues 290–350 of hNEIL1 are important for the interaction; hHus1, hRad1, and hRad9 individually and as a complex significantly stimulate NEIL1 glycosylase activity; NEIL1 foci co-localize with Rad9 foci after H2O2 treatment. Co-IP, GST pulldown, glycosylase activity assays, nuclear foci co-localization Nucleic acids research High 17395641
2007 The 9-1-1 complex physically interacts with and stimulates TDG glycosylase; hHus1 interaction maps to TDG residues 67–110 (Val74 critical); 9-1-1 stimulates TDG's removal of U and T from mispairs; interaction enhanced by MNNG treatment. Co-IP, GST pulldown, mutagenesis, glycosylase activity assays, nuclear foci co-localization Nucleic acids research High 17855402
2007 Jab1 (COP9 signalosome component) physically associates with the 9-1-1 complex via direct interaction with Rad1; Jab1 translocates the 9-1-1 complex from nucleus to cytoplasm and mediates its degradation via the 26S proteasome, suppressing checkpoint signaling. Co-IP, subcellular fractionation, proteasome inhibitor assays, checkpoint assays Journal of molecular biology Medium 17583730
2007 Hus1 loss in conditional knockout mouse fibroblasts causes spontaneous chromosomal breaks preferentially at common fragile sites during S phase, associated with γH2AX accumulation; p53 deletion does not rescue proliferation or apoptosis, implicating p53-independent mechanisms. Conditional Cre-mediated knockout, chromosomal aberration analysis, γH2AX staining, fragile site analysis Molecular biology of the cell High 17215515
2007 The 9-1-1 complex interacts with APE1 in vitro and in vivo and stimulates its AP-endonuclease activity; 9-1-1 also stimulates long-patch BER reconstituted in vitro, specifically by enhancing the early components APE1 and Pol beta. Co-IP, in vitro APE1 activity assays, reconstituted LP-BER assays Nucleic acids research High 17426133
2009 Crystal structure of the human 9-1-1 complex determined at 3.0–3.2 Å reveals a toroidal PCNA-like architecture with asymmetric subunit interfaces; biochemical analysis reveals a single repair enzyme-binding site on 9-1-1 that is competitively blocked by p21(cip1/waf1). X-ray crystallography, biochemical competition assays Molecular cell High 19446481
2009 Crystal structure of human Rad9(1-272)-Hus1-Rad1 at 2.5 Å shows a closed toroidal ring; the C-terminal tail of Rad9 regulates DNA binding, as deletion of this tail (9(ΔC)-1-1) enables stable complex formation with 5'-recessed DNA whereas full-length 9-1-1 does not. X-ray crystallography, DNA binding assays with purified proteins Journal of molecular biology High 19464297
2009 The 9-1-1 complex interacts with and stimulates hOGG1 glycosylase activity; individual subunits (hRad9, hRad1, hHus1) each enhance 8-oxoG excision and beta-elimination by hOGG1 and promote covalent OGG1-DNA intermediate formation. Co-IP, GST pulldown, in vitro glycosylase and trapping assays, cellular 8-oxoG measurement DNA repair High 19615952
2010 Casein kinase 2 (CK2) specifically phosphorylates Ser-341 and Ser-387 in the C-terminal tail of Rad9 within the 9-1-1 complex; both phosphorylations are required for efficient 9-1-1 interaction with TopBP1 and for ATR-dependent checkpoint function. In vitro kinase assay, mutagenesis, Co-IP, UV/MMS sensitivity assays Genes to cells : devoted to molecular & cellular mechanisms High 20545769
2010 Rad17 mediates the interaction between 9-1-1 and TopBP1; ATP binding to Rad17 is essential for 9-1-1/TopBP1 association; ATP hydrolysis by Rad17 is necessary for 9-1-1 loading onto DNA and elevated TopBP1 chromatin accumulation; a 9-1-1 mutant unable to bind TopBP1 still promotes TopBP1 chromatin accumulation, indicating distinct steps. Xenopus egg extract biochemistry, Rad17 ATP-binding and hydrolysis mutants, chromatin fractionation Molecular biology of the cell High 20110345
2010 Each subunit of the human 9-1-1 complex physically interacts with hMSH2, hMSH3, and hMSH6; 9-1-1 stimulates hMutSα DNA binding to G/T-containing substrates; Rad9 knockdown causes MSH6 mislocalization to the cytoplasm. Co-IP, DNA binding stimulation assays, siRNA knockdown, immunofluorescence DNA repair Medium 20188637
2010 ATR phosphorylates Rad1 (T5) and Hus1 (S219, T223) in a TopBP1-dependent manner in Xenopus egg extracts; these phosphorylations are independent of Claspin and the Rad9 C-terminus, establishing them as a Claspin-independent readout of ATR activity. Xenopus egg extract biochemistry, mutagenesis, kinase assays Molecular biology of the cell High 16436514
2011 WRN helicase physically interacts with the 9-1-1 complex via binding of the RAD1 subunit to the N-terminal region of WRN; this interaction mediates WRN relocalization to nuclear foci and ATR/TopBP1-dependent WRN phosphorylation in response to replication arrest. Co-IP, siRNA knockdown, immunofluorescence, kinase assays Oncogene Medium 22002307
2012 EM reconstruction of the human 9-1-1/FEN1/DNA ternary complex at 18-Å resolution shows that 9-1-1 orients FEN1 and double-flap DNA differently from PCNA, providing inherent stability for DNA repair versus PCNA's inherent flexibility for replication. Single-particle electron microscopy, molecular dynamics simulations, structural comparison Proceedings of the National Academy of Sciences of the United States of America High 22586102
2013 Hus1 conditional deletion in mouse testicular germ cells causes meiotic DSB repair defects (persistent γH2AX and RAD51), synapsis defects, and structural chromosome abnormalities; RAD9 localizes to RAD51-containing foci on meiotic chromosomes in a Hus1-dependent manner; RAD1 and TOPBP1 localize to the XY body independently of HUS1. Conditional knockout, meiotic chromosome spreads, immunofluorescence, fertility assays PLoS genetics High 23468651
2014 The 9-1-1/TopBP1 interaction promotes ATR activation and induces further TopBP1 accumulation at UV damage sites through a positive feedback mechanism; UV-induced Rad9 chromatin localization is independent of TopBP1, but TopBP1 redistribution to damage sites is delayed without the 9-1-1/TopBP1 interaction. Laser micro-irradiation, co-IP, ATR inhibitor, mutant TopBP1-binding-deficient Rad9 DNA repair Medium 25091155
2015 Structure-function analysis mapped a HUS1-RAD9A interface residue critical for 9-1-1 clamp assembly and DNA loading; positively charged inner ring residues of HUS1 are crucial for chromatin localization and ATR signaling; two hydrophobic pockets on the HUS1 outer surface mediate interactions with effectors (e.g. MYH) independently of checkpoint signaling. Mutagenesis, co-IP, genotoxin sensitivity assays, CHK1 phosphorylation assays The Journal of biological chemistry High 25911100
2015 The Hus1 interdomain connecting loop (residues 134–155) is a key determinant of MYH binding; the N-terminal and C-terminal halves of Hus1 both interact with and stimulate MYH; Hus1(K136A) retains MYH binding but cannot stimulate MYH glycosylase activity; Hus1 N-terminal domain (but not C-terminal half) binds DNA. Deletion mutagenesis, in vitro binding assays, glycosylase activity assays, DNA binding assays DNA repair High 26021743
2015 SIRT6 interacts with the 9-1-1 clamp (including Hus1); this interaction is enhanced after oxidative stress; APE1 and Hus1 act together to stabilize the MYH/SIRT6 complex; SIRT6, APE1, and Hus1 bind overlapping but non-competing sites on the MYH IDC. Co-IP, GST pulldown, mutagenesis, oxidative stress response assays BMC molecular biology Medium 26063178
2015 The Rad9 C-terminal tail intramolecularly binds the 9-1-1 core ring structure (CRS) via a 15-aa stretch containing two conserved consecutive phenylalanine residues, inhibiting DNA binding; TopBP1 binds the same 15-aa stretch and competes with CRS, suggesting that TopBP1 binding releases autoinhibition of DNA binding. Purified protein binding assays, deletion mutants, competitive binding with TopBP1 The Journal of biological chemistry High 26088138
2018 SUMO-1 modification of FEN1 in response to replication fork-stalling agents promotes its interaction with HUS1 (within the 9-1-1 complex) instead of PCNA; FEN1 mutations preventing SUMO-1 modification impair HUS1 interaction and rescue of stalled replication forks. SUMOylation assays, co-IP, site-directed mutagenesis, fork restart assays, genotoxin sensitivity Journal of molecular cell biology High 30184152
2019 Crystal structure of the 9-1-1 complex bound to a RHINO peptide shows RHINO binds the edge and back of the ring through specific interactions with the RAD1 subunit, establishing that 9-1-1 is a functionally double-faced DNA clamp. X-ray crystallography The Journal of biological chemistry High 31776186
2020 SIRT6 is recruited early to oxidatively damaged telomeres and subsequently recruits MYH and Hus1; Hus1 recruitment to damaged telomeres is partially dependent on SIRT6; the SIRT6/MYH/9-1-1 complex maintains telomere integrity and SIRT6 catalytic activity is required for MYH (but not SIRT6 itself) recruitment. Laser micro-irradiation at telomeres, knockout cells, immunofluorescence, time-course recruitment assays Aging Medium 32991318
2024 In Xenopus egg extracts, MRN and 9-1-1 redundantly stimulate Dna2-dependent long-range DSB end resection and ATR activation; 9-1-1 is dispensable for bulk Dna2 loading but TopBP1 loading is interdependent with 9-1-1; ATR facilitates Mre11 phosphorylation and ATM dissociation. Xenopus egg extract biochemistry, immunodepletion, DNA substrate assays, kinase assays Nucleic acids research High 38349040
2008 In Hus1-deficient cells, etoposide treatment upregulates BH3-only proteins Bim and Puma; Rad9 is released from chromatin into the cytoplasm where it binds Bcl-2, augmenting mitochondrial apoptosis; combined Bim/Puma knockdown rescues survival, placing HUS1 upstream of the intrinsic apoptotic pathway. Knockout MEFs, siRNA knockdown, subcellular fractionation, co-IP, Western blot Oncogene Medium 18794804
2025 A genome-wide CRISPR screen identified 9-1-1 (RAD9A-HUS1-RAD1) as essential for survival of BRCA2-deficient cells through an ATR-independent mechanism; loss of 9-1-1 leads to EXO1-mediated pathological expansion of PRIMPOL-dependent ssDNA gaps and requires POLζ for gap filling. Genome-wide CRISPR screen, genetic epistasis, ssDNA gap assays, EXO1 depletion rescue 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 385 17575048
2004 Dial 9-1-1 for DNA damage: the Rad9-Hus1-Rad1 (9-1-1) clamp complex. DNA repair 256 15279787
2007 The Rad9-Hus1-Rad1 checkpoint clamp regulates interaction of TopBP1 with ATR. The Journal of biological chemistry 231 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 81 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
2007 The human checkpoint sensor Rad9-Rad1-Hus1 interacts with and stimulates DNA repair enzyme TDG glycosylase. Nucleic acids research 55 17855402
2010 A structural hinge in eukaryotic MutY homologues mediates catalytic activity and Rad9-Rad1-Hus1 checkpoint complex interactions. Journal of molecular biology 54 20816984
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
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 49 23468651
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 32 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
2002 Identification and characterization of a paralog of human cell cycle checkpoint gene HUS1. Genomics 28 11944979
2015 Distinct functional consequences of MUTYH variants associated with colorectal cancer: Damaged DNA affinity, glycosylase activity and interaction with PCNA and Hus1. DNA repair 27 26377631
2007 Jab1 mediates protein degradation of the Rad9-Rad1-Hus1 checkpoint complex. Journal of molecular biology 27 17583730
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 26 27301589
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
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
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 22 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 22 24062075
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 4 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 1 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