Catalytic activity:ATP + (deoxyribonucleotide) (n) + (deoxyribonucleotide) (m) = AMP + diphosphate + (deoxyribonucleotide) (n+m) . ,cofactor:Magnesium. ,Disease:Defects in LIG4 are a cause of severe combined immunodeficiency autosomal recessive T-cell-negative/B-cell-negative/NK-cell-positive with sensitivity to ionizing radiation (RSSCID) [MIM:602450]. SCID refers to a genetically and clinically heterogeneous group of rare congenital disorders characterized by impairment of both humoral and cell-mediated immunity , leukopenia , and low or absent antibody levels. Patients with SCID present in infancy with recurrent , persistent infections by opportunistic organisms. The common characteristic of all types of SCID is absence of T-cell-mediated cellular immunity due to a defect in T-cell development. Individuals affected by RS-SCID show defects in the DNA repair machinery necessary for coding joint formation and the completion of V (D) J recombination. A subset of cells from such patients show increased radiosensitivity. ,Disease:Defects in LIG4 are the cause of LIG4 syndrome [MIM:606593]. This disease is characterized by immunodeficiency and developmental and growth delay. Patients display unusual facial features , microcephaly , growth and/or developmental delay , pancytopenia , and various skin abnormalities. ,Function:Efficiently joins single-strand breaks in a double-stranded polydeoxynucleotide in an ATP-dependent reaction. Involved in DNA non-homologous end joining (NHEJ) required for double-strand break repair and V (D) J recombination. The LIG4-XRCC4 complex is responsible for the NHEJ ligation step , and XRCC4 enhances the joining activity of LIG4. Binding of the LIG4-XRCC4 complex to DNA ends is dependent on the assembly of the DNA-dependent protein kinase complex DNA-PK to these DNA ends. ,online information:DNA ligase entry ,online information:LIG4 mutation db ,similarity:Belongs to the ATP-dependent DNA ligase family. ,similarity:Contains 2 BRCT domains. ,subunit:Binds to XRCC4. The LIG4-XRCC4 complex has probably a 1:2 stoichiometry. The LIG4-XRCC4 heteromer associates in a DNA-dependent manner with the DNA-dependent protein kinase complex DNA-PK , formed by the Ku p70/p86 dimer (G22P1/G22P2) and PRKDC. ,tissue specificity:Testis , thymus , prostate and heart. ,
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