Affinage

XRCC4

DNA repair protein XRCC4 · UniProt Q13426

Length
336 aa
Mass
38.3 kDa
Annotated
2026-04-28
100 papers in source corpus 43 papers cited in narrative 43 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

XRCC4 is a central scaffold protein of the non-homologous end joining (NHEJ) pathway that coordinates double-strand break repair and V(D)J recombination by nucleating the assembly of the core ligation machinery at DNA ends. XRCC4 forms a constitutive homodimer whose elongated coiled-coil binds asymmetrically to the inter-BRCT linker of DNA ligase IV in a 2:1 stoichiometry, stabilizing ligase IV protein levels and stimulating its adenylation and ligation activity, including ligation of incompatible DNA ends (PMID:9242410, PMID:11702069, PMID:14607114, PMID:17290226). Ku70/80 recruits the XRCC4–ligase IV complex to DNA ends, while CK2 phosphorylation of XRCC4 creates docking sites recognized by the FHA domains of PNKP and APLF, coupling end-processing to ligation; XRCC4 also co-assembles with XLF into sliding filaments that bridge and align broken DNA molecules, an activity regulated by DNA-PK/ATM phosphorylation of the XRCC4 and XLF C-terminal tails (PMID:10757784, PMID:15385968, PMID:26519825, PMID:27437582, PMID:28500754). Nuclear localization of XRCC4 depends on SUMOylation at K210 and on its interaction with ligase IV, and damage-induced K63-linked polyubiquitylation by FBXW7 enhances XRCC4–Ku association to promote NHEJ (PMID:16478998, PMID:26774286, PMID:24984242).

Mechanistic history

Synthesis pass · year-by-year structured walk · 16 steps
  1. 1995 High

    Identifying XRCC4 as a gene required for both V(D)J recombination and DSB repair established that a previously unknown nuclear factor was essential for the final joining step of NHEJ.

    Evidence cDNA cloning and functional complementation of the XRCC4-deficient XR-1 CHO cell line

    PMID:8548796

    Open questions at the time
    • No binding partners or biochemical activity identified
    • Mechanism of action unknown
  2. 1997 High

    Discovery that XRCC4 directly binds and stimulates DNA ligase IV, and that their interaction maps to the ligase IV C-terminal BRCT region, defined XRCC4's primary molecular role as a ligase IV cofactor.

    Evidence Co-IP, yeast two-hybrid, and in vitro ligation assays with purified recombinant proteins; co-purification and adenylation assays

    PMID:9242410 PMID:9259561 PMID:9352367

    Open questions at the time
    • Precise binding interface not resolved
    • Stoichiometry uncertain
    • How the complex is recruited to DSBs unknown
  3. 1998 High

    Mapping the ligase IV binding site to the inter-BRCT linker (not the BRCT domains themselves) and showing XRCC4 is a DNA-PK substrate placed XRCC4 in a regulated signaling context at DSBs.

    Evidence Systematic deletion analysis with co-IP; in vitro kinase assay with purified DNA-PK; yeast ortholog LIF1 disruption phenocopying lig4 mutants

    PMID:9430729 PMID:9670033 PMID:9705934

    Open questions at the time
    • Functional consequence of DNA-PK phosphorylation unknown
    • In vivo recruitment mechanism unresolved
  4. 1999 High

    Demonstrating that XRCC4 stabilizes ligase IV at the protein level and that XRCC4 binds DNA with preference for nicked/broken ends separated its stabilization function from its DNA-end recognition activity.

    Evidence Western/Northern blot in XR-1 cells with XRCC4 complementation; DNA-binding assays and in vitro ligation with separation-of-function mutants

    PMID:10047779 PMID:10202163

    Open questions at the time
    • DNA-binding surface not structurally defined
    • How DNA binding contributes to in vivo repair unclear
  5. 2000 High

    Crystal structure of XRCC4, combined with reconstitution of Ku-dependent end recruitment and DNA bridging by XRCC4–ligase IV, established the architectural framework of the NHEJ ligation complex and showed that Ku is the DNA-end recruiter.

    Evidence X-ray crystallography at 2.7 Å; in vitro reconstitution with Ku and DNA-PKcs showing 20-fold ligation stimulation; genetic epistasis in XRCC4/p53 double-KO mice

    PMID:10757784 PMID:10786799 PMID:10854421 PMID:11080143

    Open questions at the time
    • Structure of the XRCC4–ligase IV complex not yet solved
    • Stoichiometry in vivo debated (tetramer vs. dimer)
  6. 2001 High

    The crystal structure of the XRCC4–ligase IV inter-BRCT linker complex revealed how one ligase IV chain binds asymmetrically to the XRCC4 dimer, unwinding the coiled-coil to create a flat interface — resolving the binding mode.

    Evidence X-ray crystallography of the binary complex

    PMID:11702069

    Open questions at the time
    • Role of BRCT2 contacts not captured at this resolution
    • How tetramerization and ligase IV binding are regulated not clear
  7. 2003 High

    Establishing 2:1 XRCC4 dimer:ligase IV stoichiometry and mutual exclusivity with tetramerization resolved a structural ambiguity, while showing that DNA-PK phosphorylation sites on XRCC4 are dispensable for survival and V(D)J recombination raised the question of what these modifications do.

    Evidence Equilibrium sedimentation and size-exclusion chromatography; mass spectrometry phosphosite mapping with alanine mutagenesis and functional assays

    PMID:14599745 PMID:14607114

    Open questions at the time
    • Functional role of DNA-PK phosphorylation on XRCC4 unresolved
    • Whether tetramer has any physiological role unclear
  8. 2004 High

    Identification of CK2-phosphorylated XRCC4 as the bridge linking PNKP to the ligation complex, and demonstration that DNA-PKcs drives XRCC4–ligase IV mobilization to DSBs, established XRCC4 as an actively regulated scaffold coupling end-processing with ligation.

    Evidence Co-IP, phosphopeptide binding with FHA domain, cellular repair kinetics; biochemical fractionation with siRNA knockdown

    PMID:15385968 PMID:15520013

    Open questions at the time
    • Structural basis of CK2-phospho-XRCC4/PNKP FHA interaction not visualized
    • Temporal ordering of CK2 vs. DNA-PK phosphorylation events unclear
  9. 2006 High

    Discovery that SUMOylation at K210 is required for XRCC4 nuclear localization, that ligase IV also controls XRCC4 import, and that XLF is a new XRCC4-interacting NHEJ factor expanded the regulatory and compositional complexity of the NHEJ ligation complex.

    Evidence In vivo SUMOylation assay with K210R mutagenesis and subcellular fractionation; co-IP and siRNA of XLF; direct Ku70–XRCC4 interaction by live-cell imaging

    PMID:16439205 PMID:16478998 PMID:17124166

    Open questions at the time
    • Whether SUMOylation is damage-regulated unknown
    • Structural basis of XLF–XRCC4 interaction not yet determined
  10. 2007 High

    Showing that XRCC4–ligase IV can ligate fully incompatible DNA ends and contributes to class switch recombination in B cells defined the remarkably flexible substrate scope and broader immune function of the complex.

    Evidence In vitro ligation with defined incompatible substrates; B-cell-specific conditional XRCC4 knockout mouse with CSR assay

    PMID:17290226 PMID:17606631

    Open questions at the time
    • How the complex accommodates mismatched ends structurally unknown
    • Relative contribution of XRCC4/NHEJ vs. alternative end joining in CSR debated
  11. 2009 High

    A higher-resolution XRCC4–ligase IV BRCT structure revealed that BRCT2 makes essential contacts, refining the interface beyond the inter-BRCT linker model.

    Evidence X-ray crystallography with cellular complementation and dominant-negative overexpression

    PMID:19332554

    Open questions at the time
    • Full-length ligase IV–XRCC4 structure lacking
    • How Ku docking alters the interface unknown
  12. 2011 High

    Crystal structures of XRCC4–XLF filaments revealed alternating head-to-head interactions forming a super-helical DNA-binding channel, establishing a structural paradigm for how NHEJ factors bridge and align broken ends.

    Evidence X-ray crystallography, SAXS, EM, site-directed mutagenesis, and isothermal titration calorimetry from two independent groups

    PMID:21768349 PMID:21775435

    Open questions at the time
    • Whether filaments form in vivo at physiological concentrations unknown
    • How filament assembly is regulated by phosphorylation not determined
  13. 2015 High

    Identification of FBXW7-mediated K63-polyubiquitylation of XRCC4 at K296 (triggered by DNA-PKcs phosphorylation of S325/326 and ATM phosphorylation of FBXW7) enhancing Ku association, together with APLF FHA recognition of phospho-XRCC4, revealed a multi-layered PTM code on XRCC4 that fine-tunes NHEJ complex assembly.

    Evidence Mass spectrometry, ubiquitylation assays, mutagenesis, clonogenic survival; crystal structure of phospho-XRCC4–APLF FHA complex

    PMID:26519825 PMID:26774286

    Open questions at the time
    • Whether K63-Ub serves as a platform for additional factor recruitment unknown
    • Interplay between SUMOylation, ubiquitylation, and phosphorylation not integrated
  14. 2016 High

    Single-molecule visualization of XRCC4–XLF complexes sliding along DNA and bridging two DNA molecules provided direct biophysical evidence for the mobile-sleeve model of end synapsis.

    Evidence Dual- and quadruple-trap optical tweezers with fluorescence microscopy

    PMID:27437582

    Open questions at the time
    • Behavior in the context of chromatin and full NHEJ machinery not examined
    • How sliding converts to stable synapsis for ligation unknown
  15. 2017 High

    Phospho-mimicking mutations in XRCC4/XLF C-terminal tails selectively ablated DNA bridging without affecting ligase IV stimulation, demonstrating that DNA-PK/ATM phosphorylation separates the bridging and ligation-support functions; structural characterization of the PNKP–XRCC4–LigIV ternary complex by SAXS/HDX-MS defined multi-point contacts enabling coupled end-processing.

    Evidence Systematic mutagenesis of 14 phospho-sites with separation-of-function assays; SAXS, HDX-MS, and reconstitution of ternary complex

    PMID:28453785 PMID:28500754

    Open questions at the time
    • Identity of the kinase(s) responsible for each site in vivo not fully resolved
    • Cryo-EM or crystal structure of full synaptic complex lacking
  16. 2021 Medium

    The finding that RIG-I competes with LIG4/XLF for XRCC4 binding, suppressing NHEJ while XRCC4 reciprocally enhances RIG-I innate immune signaling, revealed an unexpected crosstalk between DNA repair and antiviral immunity.

    Evidence Co-IP, DSB recruitment assay, in vitro ligation, RNA virus replication assay, mouse model

    PMID:33846346

    Open questions at the time
    • Physiological contexts where this competition is dominant unknown
    • Whether RIG-I interaction is direct or mediated by RNA/DNA intermediates not fully resolved
    • Independent replication needed

Open questions

Synthesis pass · forward-looking unresolved questions
  • A high-resolution structure of the complete NHEJ synaptic complex — XRCC4–ligase IV–XLF filament assembled on DNA ends with Ku and DNA-PKcs — has not been determined, leaving the architecture of end synapsis and the mechanism by which phosphorylation-induced filament disassembly triggers ligation unresolved.
  • No cryo-EM or crystal structure of the full synaptic complex
  • Temporal sequence of PTM events during a single repair event not mapped in real time
  • Whether XRCC4–XLF filaments form on chromatin substrates in vivo remains undemonstrated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 4 GO:0003677 DNA binding 3 GO:0060090 molecular adaptor activity 3
Localization
GO:0005634 nucleus 4 GO:0005654 nucleoplasm 1
Pathway
R-HSA-73894 DNA Repair 8 R-HSA-1266738 Developmental Biology 2 R-HSA-168256 Immune System 2
Partners
APLFFBXW7LIG4PNKPPRKDCXLFXRCC5XRCC6
Complex memberships
Ku–XRCC4–ligase IVXRCC4–DNA ligase IVXRCC4–XLF filamentXRCC4–ligase IV–PNKP

Evidence

Reading pass · 43 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1995 XRCC4 encodes a novel nuclear protein required for completion of V(D)J recombination (both coding and signal joints) and DNA double-strand break repair, as demonstrated by functional complementation of XRCC4-deleted XR-1 CHO cells. cDNA cloning, functional complementation of mutant cell line, V(D)J recombination assay Cell High 8548796
1997 XRCC4 directly interacts with DNA ligase IV and stimulates its ligation activity 5–8 fold, establishing that XRCC4's biological function is primarily to potentiate DNA ligase IV for double-strand break ligation and V(D)J recombination. Co-immunoprecipitation, yeast two-hybrid, in vitro ligation assay with purified recombinant proteins Nature High 9242410
1997 XRCC4 interacts with DNA ligase IV via the ligase IV carboxy-terminal extension containing tandem BRCT motifs, and XRCC4 is a nuclear phosphoprotein that serves as an efficient substrate for DNA-PK in vitro. Co-immunoprecipitation, co-purification over multiple chromatographic steps, adenylylation assay, in vitro kinase assay Current Biology High 9259561
1997 XRCC4 forms a homodimer in vivo with the dimerization domain mapping to amino acids 115–204, and the core domain required for V(D)J recombination comprises amino acids 18–204. Yeast two-hybrid, deletion mutagenesis, transient V(D)J recombination assay International Immunology Medium 9352367
1998 DNA ligase IV binds XRCC4 via a region located between (not within) its two BRCT domains; this inter-BRCT linker region is necessary and sufficient for XRCC4 binding. Deletion analysis of ligase IV, co-immunoprecipitation Current Biology High 9705934
1998 XRCC4 is phosphorylated in vitro by DNA-PK (and an unidentified kinase) on serine/threonine residues within its C-terminal 130 amino acids, and XRCC4 facilitates Ku binding to DNA, promoting DNA-PK complex assembly. In vitro kinase assay with recombinant proteins, Sf9 insect-cell expression, DNA-binding assay Journal of Biological Chemistry Medium 9430729
1998 The yeast XRCC4 ortholog LIF1 interacts with the C-terminal BRCT domain of yeast Lig4, occurs as a Lig4-LIF1 heterodimer in vivo, stabilizes Lig4, and is required for non-homologous end joining; LIF1 disruption phenocopies lig4 mutants. Yeast two-hybrid, gene disruption, plasmid end-joining assay, Western blot for protein stability EMBO Journal High 9670033
1999 XRCC4 is required to stabilize DNA ligase IV protein (not mRNA) in cells; in XRCC4-deficient XR-1 cells, ligase IV protein is nearly undetectable, and reintroduction of XRCC4 restores ligase IV to wild-type levels. Western blot for protein levels, Northern blot for mRNA, complementation of XR-1 cells Mutation Research High 10047779
1999 XRCC4 binds DNA with preference for nicked or broken ends; the DNA-binding activity correlates with complementation of V(D)J recombination defects but is not required for stimulation of DNA ligase IV adenylation. DNA-binding assay, in vitro ligation assay, complementation of XRCC4-deficient cells EMBO Journal High 10202163
2000 XRCC4 crystal structure reveals an elongated dumbbell-shaped tetramer with an N-terminal globular head containing a putative DNA-binding HTH motif and a long C-terminal coiled-coil stalk that mediates ligase IV interaction and tetramerization. X-ray crystallography at 2.7 Å resolution EMBO Journal High 11080143
2000 The XRCC4-ligase IV complex directly binds Ku at DNA ends; Ku is required to recruit XRCC4-ligase IV to DNA ends, and this recruitment stimulates the initial ligation rate 20-fold in vitro. Direct protein-protein interaction assay, in vitro ligation assay, DNA-binding assay Molecular and Cellular Biology High 10757784
2000 DNA ligase IV-XRCC4 complex binds specifically to DNA ends and can act as a bridging factor linking DNA molecules; DNA-PKcs (but not Ku alone) stimulates intermolecular ligation by the complex. In vitro ligation assay, DNA end-binding assay, protein-protein interaction at DNA ends Journal of Biological Chemistry High 10854421
2000 p53 deficiency rescues embryonic lethality and neuronal apoptosis caused by XRCC4 deficiency in mice, placing XRCC4 upstream of p53-dependent apoptosis; XRCC4-null/p53-null mice develop pro-B-cell lymphomas with IgH-c-myc translocations. Genetic epistasis in double-knockout mice, tumor analysis, cytogenetics Nature High 10786799
2001 Crystal structure of XRCC4 bound to the inter-BRCT linker peptide of DNA ligase IV reveals that one ligase chain binds asymmetrically to an XRCC4 dimer; XRCC4 helical tails form a coiled-coil that unwinds upon ligase binding, creating a flat interaction surface stabilized by charged hydrogen bonds and hydrophobic contacts. X-ray crystallography Nature Structural Biology High 11702069
2003 DNA-PK phosphorylates XRCC4 at serines 260 and 318 in the C-terminal region in vitro, but substitution of all phosphorylation sites to alanine does not impair cell survival after ionizing radiation or V(D)J recombination. Mass spectrometry mapping, site-directed mutagenesis, clonogenic survival assay, V(D)J recombination assay DNA Repair High 14599745
2003 XRCC4 dimer binds DNA ligase IV in a 2:1 stoichiometry in solution; tetramerization of XRCC4 and DNA ligase IV binding are mutually exclusive because they share overlapping interfaces. Equilibrium sedimentation, mutational analysis, size-exclusion chromatography Journal of Molecular Biology High 14607114
2004 XRCC4 physically links polynucleotide kinase (PNK) to DNA ligase IV: CK2-phosphorylated XRCC4 is recognized by the FHA domain of PNK, and disruption of this interaction in vivo increases radiosensitivity and slows DSB repair kinetics. Co-immunoprecipitation, phosphopeptide binding, in vitro end-joining assay, cellular repair kinetics EMBO Journal High 15385968
2004 DSB induction causes DNA-PK-dependent phosphorylation and mobilization of XRCC4-ligase IV from the soluble nucleoplasm to a less-extractable nuclear fraction; DNA-PKcs is required for XRCC4-ligase IV complex recruitment, and ligase IV is needed for stable XRCC4 recruitment. Biochemical fractionation, co-immunoprecipitation, siRNA knockdown in human cells, laser-induced DSBs Journal of Biological Chemistry High 15520013
2006 XRCC4 is SUMOylated at lysine 210; this modification is required for nuclear localization of XRCC4, and a SUMOylation-deficient mutant remains cytoplasmic, causes radiation sensitivity, and fails to support V(D)J recombination. In vitro and in vivo SUMOylation assay, site-directed mutagenesis, subcellular fractionation, clonogenic survival, V(D)J assay Molecular and Cellular Biology High 16478998
2006 XLF (XRCC4-like factor/Cernunnos) directly interacts with the XRCC4-ligase IV complex in vitro and in vivo; siRNA depletion of XLF causes radiosensitivity and impaired NHEJ, identifying XLF as a core NHEJ component. Co-immunoprecipitation, in vitro pulldown, siRNA knockdown, clonogenic survival, NHEJ assay Cell High 16439205
2006 Cernunnos/XLF physically interacts with the XRCC4-ligase IV complex and is the human homolog of yeast Nej1, connecting the NHEJ ligation complex across eukaryotes. Co-immunoprecipitation, sequence analysis, structural prediction Journal of Biological Chemistry Medium 16571728
2006 XRCC4 directly interacts with Ku70, and XRCC4-ligase IV accumulation at DSBs depends on Ku70/80 but not DNA-PKcs, suggesting Ku serves as a flexible tether between Ku70/80 and ligase IV via XRCC4. Pulsed near-IR laser DSB induction, live-cell imaging (FRAP), direct protein-protein interaction assay PNAS High 17124166
2007 XRCC4:DNA ligase IV can ligate two DNA ends with fully incompatible 3' overhangs (no base pairing) and can ligate across 1 nt gaps; this intrinsic flexibility of the complex explains in vivo end-joining at mismatched ends. In vitro ligation assay with defined incompatible DNA substrates, purified human XRCC4:Lig4 EMBO Journal High 17290226
2007 XRCC4 plays a role in immunoglobulin class switch recombination (CSR); B-lymphocyte-specific conditional XRCC4 knockout reduces CSR approximately 2-fold in vivo and in vitro. Conditional knockout mouse (loxP/Cre), in vivo and in vitro CSR assay Journal of Experimental Medicine High 17606631
2007 Ku interacts with DNA ligase IV via the first BRCT motif of ligase IV; this interaction is enhanced by XRCC4 and dsDNA; DNA-PK kinase activity causes disassembly of the Ku/DNA ligase IV/XRCC4 complex. Pulldown assay, deletion mapping, in vitro kinase assay DNA Repair Medium 17241822
2008 XLF promotes re-adenylation of the ligase IV-XRCC4 complex after ligation, allowing in situ recharging of ligase IV to facilitate double-strand ligation by a single complex; XLF is a weakly bound partner of the tight LX complex. Biochemical adenylation assay, in vitro ligation assay, cellular DSB repair kinetics Nucleic Acids Research High 19056826
2008 Werner protein (WRN) physically interacts with the XRCC4-DNA ligase IV complex; this interaction stimulates WRN exonuclease (but not helicase) activity, and WRN-processed substrates are subsequently ligated by XRCC4-ligase IV, coordinating end processing with ligation. Co-immunoprecipitation, in vitro exonuclease assay, in vitro ligation assay Biochemistry Medium 18558713
2009 High-resolution crystal structure of human XRCC4 bound to the tandem BRCT repeat of DNA ligase IV reveals an extensive binding interface formed by a helix-loop-helix in the inter-BRCT linker plus significant contacts from the second BRCT domain, inducing a kink in the XRCC4 tail; interaction with the second BRCT domain is necessary for stable binding in cells. X-ray crystallography, cellular complementation, dominant-negative overexpression Molecular and Cellular Biology High 19332554
2010 Unphosphorylated XRCC4 interacts with the catalytic domain of PNKP (stimulating PNKP turnover), while CK2-phosphorylated XRCC4 binds the PNKP FHA domain with high affinity but inhibits PNKP activity; the XRCC4-ligase IV complex also stimulates PNKP turnover independently of XRCC4 phosphorylation. In vitro kinase assay, pulldown/co-IP, in vitro PNKP activity assay Journal of Biological Chemistry Medium 20852255
2010 DNA ligase IV controls nuclear localization and stability of XRCC4: in ligase IV-deficient cells, XRCC4 remains cytoplasmic even after DSB induction; ligase IV also regulates nuclear import of XLF. Subcellular fractionation, immunofluorescence, Western blot in ligase IV-deficient cells DNA Repair Medium 24984242
2011 XRCC4 and XLF form alternating parallel super-helical filaments via head-domain interactions (XLF Leu-115 'Leu-lock' inserts into a hydrophobic XRCC4 pocket); these filaments form a positively charged DNA-binding channel that aligns ends for ligation. X-ray crystallography, SAXS, site-directed mutagenesis, biophysical analysis Journal of Biological Chemistry High 21775435
2011 Crystal structure of XLF-XRCC4 complex at 3.94 Å confirms filament arrangement; four XRCC4 residues (Glu55, Asp58, Met61, Phe106) are essential for XLF interaction as determined by mutagenesis and calorimetry. X-ray crystallography, electron microscopy, site-directed mutagenesis, isothermal titration calorimetry PNAS High 21768349
2011 XRCC4 controls nuclear import and sub-nuclear distribution of DNA ligase IV; when co-expressed with XRCC4, ligase IV is efficiently imported and distributes like XRCC4; the XRCC4-ligase IV complex exchanges faster at DNA damage sites than XRCC4 alone. Fluorescent fusion protein expression, live-cell imaging, FRAP, nuclear fractionation DNA Repair Medium 21982441
2012 XRCC4-XLF complexes robustly bridge two independent DNA molecules; this bridging activity is DNA ligase IV-independent and suggests an early role for the complex in holding broken DNA ends together prior to ligation. DNA bridging assay, direct visualization, crystal structure at 3.94 Å, mutational analysis Nucleic Acids Research High 22287571
2014 XRCC4 undergoes M-phase-specific phosphorylation requiring CDK activity and Plk1; a phosphorylation-defective XRCC4 mutant shows more efficient M-phase DSB repair but increased anaphase bridge formation, indicating this phosphorylation suppresses NHEJ during mitosis to prevent genomic instability. Site-directed mutagenesis, kinase inhibition, live-cell imaging, chromosome analysis PLOS Genetics Medium 25166505
2015 FBXW7-mediated K63-linked polyubiquitylation of XRCC4 at lysine 296 (triggered by DNA-PKcs phosphorylation of XRCC4 at Ser325/326 after IR and ATM phosphorylation of FBXW7 at Ser26) enhances XRCC4 association with Ku70/80 to facilitate NHEJ. Co-immunoprecipitation, mass spectrometry, site-directed mutagenesis, in vivo ubiquitylation assay, clonogenic survival Molecular Cell High 26774286
2015 PAXX (paralog of XRCC4 and XLF) has a crystal structure resembling XRCC4, directly interacts with Ku (not XRCC4 directly), and is recruited to DSB sites; PAXX promotes Ku-dependent DNA ligation in vitro and functions together with XRCC4 and XLF in NHEJ. X-ray crystallography, co-immunoprecipitation, CRISPR-Cas9 knockout, in vitro ligation assay, chromatin fractionation Science High 25574025
2015 CK2-phosphorylated XRCC4 is recognized by the FHA domain of APLF; crystal structure of the phospho-XRCC4-APLF complex reveals the binding mode and shows distinct but overlapping specificities among FHA domain family members for XRCC4 vs. XRCC1 scaffolds. X-ray crystallography, NMR, biochemical binding assays DNA Repair High 26519825
2016 XRCC4-XLF complexes form mobile sleeve-like structures that can slide along DNA and bridge two independent DNA molecules; XLF stimulates XRCC4 binding to DNA, and the resulting heteromeric complexes diffuse swiftly along DNA, enabling rapid reconnection of broken ends. Dual- and quadruple-trap optical tweezers with fluorescence microscopy (single-molecule) Nature High 27437582
2017 Phospho-mimicking mutations in the C-terminal tails of both XRCC4 and XLF reduce stability and DNA-bridging capacity of XRCC4/XLF filaments without affecting their ability to stimulate ligase IV activity, indicating that DNA-PK/ATM phosphorylation of these tails specifically regulates DNA bridging. Site-directed mutagenesis (14 phosphorylation sites), in vitro DNA bridging assay, ligation stimulation assay eLife High 28500754
2017 XRCC4-ligase IV complex stimulates Artemis endonuclease activity on 3' overhangs in a DNA-PKcs-independent manner; X4-LIV and DNA-PKcs interfere with each other in stimulating Artemis, supporting sequential rather than concurrent recruitment. In vitro nuclease assay, in vitro ligation assay with defined DNA substrates Journal of Biological Chemistry Medium 28696258
2017 The PNKP-XRCC4-LigIV complex requires XRCC4 phosphorylation for stable PNKP binding (one PNKP per XRCC4 dimer); SAXS and hydrogen-deuterium exchange reveal that PNKP makes multipoint contacts with XRCC4 coiled-coil and LigIV BRCT repeats; a disease mutation E326K on the PNKP phosphatase domain surface impairs PNKP recruitment to DSBs. SAXS, HDX-MS, in vitro complex reconstitution, site-directed mutagenesis, cellular recruitment assay Nucleic Acids Research High 28453785
2021 RIG-I interacts with XRCC4 and the RIG-I/XRCC4 interaction impedes formation of the XRCC4/LIG4/XLF complex at DSBs, suppressing NHEJ; reciprocally, XRCC4 promotes RIG-I immune signaling by enhancing RIG-I oligomerization and ubiquitination. Co-immunoprecipitation, DSB recruitment assay, in vitro ligation assay, RNA virus replication assay, mouse model Nature Communications Medium 33846346

Source papers

Stage 0 corpus · 100 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 XLF interacts with the XRCC4-DNA ligase IV complex to promote DNA nonhomologous end-joining. Cell 593 16439205
1997 Activity of DNA ligase IV stimulated by complex formation with XRCC4 protein in mammalian cells. Nature 520 9242410
2000 Interplay of p53 and DNA-repair protein XRCC4 in tumorigenesis, genomic stability and development. Nature 480 10786799
1997 Mammalian DNA double-strand break repair protein XRCC4 interacts with DNA ligase IV. Current biology : CB 373 9259561
1995 The XRCC4 gene encodes a novel protein involved in DNA double-strand break repair and V(D)J recombination. Cell 371 8548796
2006 Dynamic assembly of end-joining complexes requires interaction between Ku70/80 and XRCC4. Proceedings of the National Academy of Sciences of the United States of America 319 17124166
2000 Ku recruits the XRCC4-ligase IV complex to DNA ends. Molecular and cellular biology 297 10757784
2015 DNA repair. PAXX, a paralog of XRCC4 and XLF, interacts with Ku to promote DNA double-strand break repair. Science (New York, N.Y.) 244 25574025
2001 Crystal structure of an Xrcc4-DNA ligase IV complex. Nature structural biology 202 11702069
1998 Double-strand break repair in Ku86- and XRCC4-deficient cells. Nucleic acids research 194 9826756
2004 Xrcc4 physically links DNA end processing by polynucleotide kinase to DNA ligation by DNA ligase IV. The EMBO journal 189 15385968
2000 Interactions of the DNA ligase IV-XRCC4 complex with DNA ends and the DNA-dependent protein kinase. The Journal of biological chemistry 173 10854421
1998 The XRCC4 gene product is a target for and interacts with the DNA-dependent protein kinase. The Journal of biological chemistry 153 9430729
1999 DNA binding of Xrcc4 protein is associated with V(D)J recombination but not with stimulation of DNA ligase IV activity. The EMBO journal 147 10202163
2000 Crystal structure of the Xrcc4 DNA repair protein and implications for end joining. The EMBO journal 146 11080143
1999 Absence of DNA ligase IV protein in XR-1 cells: evidence for stabilization by XRCC4. Mutation research 144 10047779
2015 Interactome analysis identifies a new paralogue of XRCC4 in non-homologous end joining DNA repair pathway. Nature communications 141 25670504
2007 Defects in XRCC4 and KU80 differentially affect the joining of distal nonhomologous ends. Proceedings of the National Academy of Sciences of the United States of America 139 18093953
2011 XRCC4 protein interactions with XRCC4-like factor (XLF) create an extended grooved scaffold for DNA ligation and double strand break repair. The Journal of biological chemistry 137 21775435
1998 Saccharomyces cerevisiae LIF1: a function involved in DNA double-strand break repair related to mammalian XRCC4. The EMBO journal 136 9670033
2007 XRCC4:DNA ligase IV can ligate incompatible DNA ends and can ligate across gaps. The EMBO journal 133 17290226
2016 Sliding sleeves of XRCC4-XLF bridge DNA and connect fragments of broken DNA. Nature 127 27437582
2012 A human XRCC4-XLF complex bridges DNA. Nucleic acids research 121 22287571
2004 DNA-dependent protein kinase and XRCC4-DNA ligase IV mobilization in the cell in response to DNA double strand breaks. The Journal of biological chemistry 119 15520013
2007 Role for DNA repair factor XRCC4 in immunoglobulin class switch recombination. The Journal of experimental medicine 118 17606631
1998 DNA ligase IV binds to XRCC4 via a motif located between rather than within its BRCT domains. Current biology : CB 115 9705934
2009 Structural and functional interaction between the human DNA repair proteins DNA ligase IV and XRCC4. Molecular and cellular biology 114 19332554
2016 FBXW7 Facilitates Nonhomologous End-Joining via K63-Linked Polyubiquitylation of XRCC4. Molecular cell 112 26774286
2002 An xrcc4 defect or Wortmannin stimulates homologous recombination specifically induced by double-strand breaks in mammalian cells. Nucleic acids research 110 12140331
2011 Structural characterization of filaments formed by human Xrcc4-Cernunnos/XLF complex involved in nonhomologous DNA end-joining. Proceedings of the National Academy of Sciences of the United States of America 107 21768349
2007 Interaction of the Ku heterodimer with the DNA ligase IV/Xrcc4 complex and its regulation by DNA-PK. DNA repair 104 17241822
2003 DNA-PK phosphorylation sites in XRCC4 are not required for survival after radiation or for V(D)J recombination. DNA repair 104 14599745
2010 XLF regulates filament architecture of the XRCC4·ligase IV complex. Structure (London, England : 1993) 98 21070942
2006 Cernunnos interacts with the XRCC4 x DNA-ligase IV complex and is homologous to the yeast nonhomologous end-joining factor Nej1. The Journal of biological chemistry 97 16571728
2007 Crystal structure of human XLF/Cernunnos reveals unexpected differences from XRCC4 with implications for NHEJ. The EMBO journal 94 18046455
2008 XLF-Cernunnos promotes DNA ligase IV-XRCC4 re-adenylation following ligation. Nucleic acids research 93 19056826
2013 XRCC4 and XLF form long helical protein filaments suitable for DNA end protection and alignment to facilitate DNA double strand break repair. Biochemistry and cell biology = Biochimie et biologie cellulaire 89 23442139
2002 Defining interactions between DNA-PK and ligase IV/XRCC4. DNA repair 89 12509254
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2006 SUMO modification of human XRCC4 regulates its localization and function in DNA double-strand break repair. Molecular and cellular biology 82 16478998
2014 Canonical non-homologous end joining in mitosis induces genome instability and is suppressed by M-phase-specific phosphorylation of XRCC4. PLoS genetics 77 25166505
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2008 Oncogenic transformation in the absence of Xrcc4 targets peripheral B cells that have undergone editing and switching. The Journal of experimental medicine 58 19064702
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2007 Variation in DNA repair genes XRCC3, XRCC4, XRCC5 and susceptibility to myeloma. Human molecular genetics 52 17901044
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2005 Radiosensitization of MDA-MB-231 breast tumor cells by adenovirus-mediated overexpression of a fragment of the XRCC4 protein. Molecular cancer therapeutics 23 16227403
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