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X-ray repair complementing defective repair in Chinese hamster cells 5 (double-strand-break rejoining)
Protein XRCC5 PDB 1jeq.png
PDB rendering based on 1jeq.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols XRCC5 ; KARP-1; KARP1; KU80; KUB2; Ku86; NFIV
External IDs OMIM194364 MGI104517 HomoloGene40681 GeneCards: XRCC5 Gene
EC number 3.6.1. EC 3.6.1.
RNA expression pattern
PBB GE XRCC5 208642 s at tn.png
PBB GE XRCC5 208643 s at tn.png
More reference expression data
Species Human Mouse
Entrez 7520 22596
Ensembl ENSG00000079246 ENSMUSG00000026187
UniProt P13010 P27641
RefSeq (mRNA) NM_021141 NM_009533
RefSeq (protein) NP_066964 NP_033559
Location (UCSC) Chr 2:
216.97 – 217.07 Mb
Chr 1:
72.31 – 72.39 Mb
PubMed search [1] [2]

Ku80 is a protein that, in humans, is encoded by the XRCC5 gene.[1] Together, Ku70 and Ku80 make up the Ku heterodimer, which binds to DNA double-strand break ends and is required for the non-homologous end joining (NHEJ) pathway of DNA repair. It is also required for V(D)J recombination, which utilizes the NHEJ pathway to promote antigen diversity in the mammalian immune system.

In addition to its role in NHEJ, Ku is required for telomere length maintenance and subtelomeric gene silencing.[2]

Ku was originally identified when patients with systemic lupus erythematosus were found to have high levels of autoantibodies to the protein.[1]


Ku80 has been referred to by several names including:

  • Lupus Ku autoantigen protein p80
  • ATP-dependent DNA helicase 2 subunit 2
  • X-ray repair complementing defective repair in Chinese hamster cells 5
  • X-ray repair cross-complementing 5 (XRCC5)

Clinical significance[edit]

A rare microsatellite polymorphism in this gene is associated with cancer in patients of varying radiosensitivity.[1]


Ku80 has been shown to interact with:


  1. ^ a b c "Entrez Gene: XRCC6 X-ray repair complementing defective repair in Chinese hamster cells 6 (Ku autoantigen, 70kDa)". 
  2. ^ Boulton SJ, Jackson SP (March 1998). "Components of the Ku-dependent non-homologous end-joining pathway are involved in telomeric length maintenance and telomeric silencing". EMBO J. 17 (6): 1819–28. doi:10.1093/emboj/17.6.1819. PMC 1170529. PMID 9501103. 
  3. ^ a b Gell D, Jackson SP (September 1999). "Mapping of protein-protein interactions within the DNA-dependent protein kinase complex". Nucleic Acids Res. 27 (17): 3494–502. doi:10.1093/nar/27.17.3494. PMC 148593. PMID 10446239. 
  4. ^ Jin S, Kharbanda S, Mayer B, Kufe D, Weaver DT (October 1997). "Binding of Ku and c-Abl at the kinase homology region of DNA-dependent protein kinase catalytic subunit". J. Biol. Chem. 272 (40): 24763–6. doi:10.1074/jbc.272.40.24763. PMID 9312071. 
  5. ^ a b c Matheos D, Ruiz MT, Price GB, Zannis-Hadjopoulos M (October 2002). "Ku antigen, an origin-specific binding protein that associates with replication proteins, is required for mammalian DNA replication". Biochim. Biophys. Acta 1578 (1-3): 59–72. doi:10.1016/s0167-4781(02)00497-9. PMID 12393188. 
  6. ^ a b Barlev NA, Poltoratsky V, Owen-Hughes T, Ying C, Liu L, Workman JL et al. (March 1998). "Repression of GCN5 histone acetyltransferase activity via bromodomain-mediated binding and phosphorylation by the Ku-DNA-dependent protein kinase complex". Mol. Cell. Biol. 18 (3): 1349–58. PMC 108848. PMID 9488450. 
  7. ^ Yang CR, Yeh S, Leskov K, Odegaard E, Hsu HL, Chang C et al. (May 1999). "Isolation of Ku70-binding proteins (KUBs)". Nucleic Acids Res. 27 (10): 2165–74. doi:10.1093/nar/27.10.2165. PMC 148436. PMID 10219089. 
  8. ^ Singleton BK, Torres-Arzayus MI, Rottinghaus ST, Taccioli GE, Jeggo PA (May 1999). "The C terminus of Ku80 activates the DNA-dependent protein kinase catalytic subunit". Mol. Cell. Biol. 19 (5): 3267–77. PMC 84121. PMID 10207052. 
  9. ^ Song K, Jung D, Jung Y, Lee SG, Lee I (September 2000). "Interaction of human Ku70 with TRF2". FEBS Lett. 481 (1): 81–5. doi:10.1016/s0014-5793(00)01958-x. PMID 10984620. 
  10. ^ Ko L, Cardona GR, Chin WW (May 2000). "Thyroid hormone receptor-binding protein, an LXXLL motif-containing protein, functions as a general coactivator". Proc. Natl. Acad. Sci. U.S.A. 97 (11): 6212–7. doi:10.1073/pnas.97.11.6212. PMC 18584. PMID 10823961. 
  11. ^ Ko L, Chin WW (March 2003). "Nuclear receptor coactivator thyroid hormone receptor-binding protein (TRBP) interacts with and stimulates its associated DNA-dependent protein kinase". J. Biol. Chem. 278 (13): 11471–9. doi:10.1074/jbc.M209723200. PMID 12519782. 
  12. ^ Ohta S, Shiomi Y, Sugimoto K, Obuse C, Tsurimoto T (October 2002). "A proteomics approach to identify proliferating cell nuclear antigen (PCNA)-binding proteins in human cell lysates. Identification of the human CHL12/RFCs2-5 complex as a novel PCNA-binding protein". J. Biol. Chem. 277 (43): 40362–7. doi:10.1074/jbc.M206194200. PMID 12171929. 
  13. ^ Balajee AS, Geard CR (March 2001). "Chromatin-bound PCNA complex formation triggered by DNA damage occurs independent of the ATM gene product in human cells". Nucleic Acids Res. 29 (6): 1341–51. doi:10.1093/nar/29.6.1341. PMC 29758. PMID 11239001. 
  14. ^ Schild-Poulter C, Pope L, Giffin W, Kochan JC, Ngsee JK, Traykova-Andonova M et al. (May 2001). "The binding of Ku antigen to homeodomain proteins promotes their phosphorylation by DNA-dependent protein kinase". J. Biol. Chem. 276 (20): 16848–56. doi:10.1074/jbc.M100768200. PMID 11279128. 
  15. ^ O'Connor MS, Safari A, Liu D, Qin J, Songyang Z (July 2004). "The human Rap1 protein complex and modulation of telomere length". J. Biol. Chem. 279 (27): 28585–91. doi:10.1074/jbc.M312913200. PMID 15100233. 
  16. ^ Chai W, Ford LP, Lenertz L, Wright WE, Shay JW (December 2002). "Human Ku70/80 associates physically with telomerase through interaction with hTERT". J. Biol. Chem. 277 (49): 47242–7. doi:10.1074/jbc.M208542200. PMID 12377759. 
  17. ^ Adam L, Bandyopadhyay D, Kumar R (January 2000). "Interferon-alpha signaling promotes nucleus-to-cytoplasmic redistribution of p95Vav, and formation of a multisubunit complex involving Vav, Ku80, and Tyk2". Biochem. Biophys. Res. Commun. 267 (3): 692–6. doi:10.1006/bbrc.1999.1978. PMID 10673353. 
  18. ^ Karmakar P, Snowden CM, Ramsden DA, Bohr VA (August 2002). "Ku heterodimer binds to both ends of the Werner protein and functional interaction occurs at the Werner N-terminus". Nucleic Acids Res. 30 (16): 3583–91. doi:10.1093/nar/gkf482. PMC 134248. PMID 12177300. 
  19. ^ Li B, Comai L (September 2000). "Functional interaction between Ku and the werner syndrome protein in DNA end processing". J. Biol. Chem. 275 (37): 28349–52. doi:10.1074/jbc.C000289200. PMID 10880505. 

Further reading[edit]