XRCC4

The protein encoded by this gene functions together with DNA ligase IV and the DNA-dependent protein kinase in the repair of DNA double-strand breaks. This protein plays a role in both non-homologous end joining and the completion of V(D)J recombination. Mutations in this gene can cause short stature, microcephaly, and endocrine dysfunction (SSMED). Alternative splicing generates several transcript variants. [provided by RefSeq, Dec 2015]

X-Ray Repair Cross Complementing 4

DNA repair protein XRCC4
DNA non-homologous end joining (NHEJ) core factor, required for double-strand break repair and V(D)J recombination (PubMed:10757784, PubMed:10854421, PubMed:17124166, PubMed:16412978, PubMed:8548796, PubMed:25742519, PubMed:12517771, PubMed:17290226, PubMed:22228831, PubMed:25597996, PubMed:25934149, PubMed:26100018, PubMed:26774286).
Acts as a scaffold protein that regulates recruitment of other proteins to DNA double-strand breaks (DSBs) (PubMed:15385968, PubMed:20852255, PubMed:26774286, PubMed:27437582).
Associates with NHEJ1/XLF to form alternating helical filaments that bridge DNA and act like a bandage, holding together the broken DNA until it is repaired (PubMed:26100018, PubMed:27437582, PubMed:28500754, PubMed:21775435, PubMed:22287571, PubMed:21768349).
The XRCC4-NHEJ1/XLF subcomplex binds to the DNA fragments of a DSB in a highly diffusive manner and robustly bridges two independent DNA molecules, holding the broken DNA fragments in close proximity to one other (PubMed:27437582).
The mobility of the bridges ensures that the ends remain accessible for further processing by other repair factors (PubMed:27437582).
Plays a key role in the NHEJ ligation step of the broken DNA during DSB repair via direct interaction with DNA ligase IV (LIG4): the LIG4-XRCC4 subcomplex reseals the DNA breaks after the gap filling is completed (PubMed:9242410, PubMed:10757784, PubMed:10854421, PubMed:12517771, PubMed:17290226, PubMed:19837014).
XRCC4 stabilizes LIG4, regulates its subcellular localization and enhances LIG4's joining activity (PubMed:9242410, PubMed:10757784, PubMed:10854421, PubMed:12517771, PubMed:17290226, PubMed:21982441, PubMed:22228831).
Binding of the LIG4-XRCC4 subcomplex to DNA ends is dependent on the assembly of the DNA-dependent protein kinase complex DNA-PK to these DNA ends (PubMed:10757784, PubMed:10854421).
Promotes displacement of PNKP from processed strand break termini (PubMed:20852255, PubMed:28453785).
Protein XRCC4, C-terminus
Acts as an activator of the phospholipid scramblase activity of XKR4 (PubMed:33725486).
This form, which is generated upon caspase-3 (CASP3) cleavage, translocates into the cytoplasm and interacts with XKR4, thereby promoting phosphatidylserine scramblase activity of XKR4 and leading to phosphatidylserine exposure on apoptotic cell surface (PubMed:33725486).

Biological Process DNA ligation involved in DNA repair Source:UniProtKB4 Publications
Biological Process double-strand break repair Source:UniProtKB1 Publication
Biological Process double-strand break repair via nonhomologous end joining Source:UniProtKB8 Publications
Biological Process immunoglobulin V(D)J recombination Source:GO_Central1 Publication
Biological Process positive regulation of ligase activity Source:UniProtKB1 Publication
Biological Process positive regulation of phosphatidylserine exposure on apoptotic cell surface Source:UniProtKB
Biological Process protein localization to site of double-strand break Source:UniProtKB1 Publication
Biological Process response to X-ray Source:UniProtKB1 Publication

Nucleus
Chromosome
Localizes to site of double-strand breaks.
Protein XRCC4, C-terminus
Cytoplasm
Translocates from the nucleus to the cytoplasm following cleavage by caspase-3 (CASP3).

Short stature, microcephaly, and endocrine dysfunction (SSMED):
A disease characterized by short stature and microcephaly apparent at birth, progressive postnatal growth failure, and endocrine dysfunction. In affected adults endocrine features include hypergonadotropic hypogonadism, multinodular goiter, and diabetes mellitus. Variable features observed in some patients are progressive ataxia, and lymphopenia or borderline leukopenia.

Phosphorylated by PRKDC at the C-terminus in response to DNA damage; Ser-260 and Ser-320 constitute the main phosphorylation sites (PubMed:9430729, PubMed:15177042, PubMed:14599745, PubMed:12547193, PubMed:26666690, PubMed:28500754, PubMed:30247612).
Phosphorylations by PRKDC at the C-terminus of XRCC4 and NHEJ1/XLF are highly redundant and regulate ability of the XRCC4-NHEJ1/XLF subcomplex to bridge DNA (PubMed:22228831, PubMed:28500754).
Phosphorylation by PRKDC does not prevent interaction with NHEJ1/XLF but disrupts ability to bridge DNA and promotes detachment from DNA (PubMed:22228831, PubMed:28500754).
Phosphorylation at Ser-327 and Ser-328 by PRKDC promotes recognition by the SCF(FBXW7) complex and subsequent ubiquitination via 'Lys-63'-linked ubiquitin (PubMed:26774286).
Phosphorylation at Thr-233 by CK2 promotes interaction with PNKP; regulating PNKP activity and localization to DNA damage sites (PubMed:15385968, PubMed:20852255, PubMed:28453785).
Phosphorylation by CK2 promotes interaction with APTX (PubMed:15380105).
Ubiquitinated at Lys-296 by the SCF(FBXW7) complex via 'Lys-63'-linked ubiquitination, thereby promoting double-strand break repair: the SCF(FBXW7) complex specifically recognizes XRCC4 when phosphorylated at Ser-327 and Ser-328 by PRKDC, and 'Lys-63'-linked ubiquitination facilitates DNA non-homologous end joining (NHEJ) by enhancing association with XRCC5/Ku80 and XRCC6/Ku70 (PubMed:26774286).
Monoubiquitinated (PubMed:16412978).
DNA repair protein XRCC4
Undergoes proteolytic processing by caspase-3 (CASP3) (Probable) (PubMed:33725486).
This generates the protein XRCC4, C-terminus (XRCC4/C), which translocates to the cytoplasm and activates phospholipid scramblase activity of XKR4, thereby promoting phosphatidylserine exposure on apoptotic cell surface (PubMed:33725486).