Disease relevance of LIG3

• Genetic polymorphisms in XRCC1 gene could, through alteration of protein structure, lead to defective functioning of DNA Polbeta, PARP and LIG3 enzymes resulting in defective DNA repair and increased risk of childhood acute lymphoblastic leukemia (ALL) [1].
• The DNA ligase III gene was localized to human chromosome 17, which eliminated this gene as a candidate for the cancer-prone disease Bloom syndrome that is associated with DNA joining abnormalities [2].
• Human DNA ligase I, but not DNA ligase III or bacteriophage T4 DNA ligase, complemented both defects in 46BR.1G1 extracts [3].
• Western blot analysis revealed that DNA ligase III was degraded in human fibrosarcoma HT1080 cells following exposure to gamma-radiation [4].
• The CHO XRCC1 mutant, EM9, deficient in DNA ligase III activity, exhibits hypersensitivity to camptothecin independent of DNA replication [5].

High impact information on LIG3

• Furthermore, we demonstrate that the excision repair pathway of an abasic site can be reconstituted on core particles using the known repair enzymes, AP-endonuclease 1, DNA polymerase beta and DNA ligase III [6].
• Furthermore, the established structure of an XRCC1 BRCT homodimer suggests potential protein-protein interaction sites for the complementary BRCT domain in DNA ligase III, since these two domains form a stable heterodimeric complex [7].
• To determine its role in DNA repair, cellular growth, and embryonic development, we introduced targeted interruption of the DNA ligase III (LIG3) gene into the mouse [8].
• This provides a mechanism for the recruitment of the DNA ligase IIIalpha-XRCC1 complex to in vivo DNA single-strand breaks and suggests that the zinc finger of DNA ligase III enables this complex and associated repair factors to locate the strand break in the presence of the negatively charged poly(ADP-ribose) polymer [9].
• PARP-1 binds directly to an N-terminal region of DNA ligase III immediately adjacent to its zinc finger [9].

Biological context of LIG3

• LIG3 mutant cells have relatively normal XRCC1 levels but elevated sister chromatid exchange [8].
• Biochemical studies suggest that the majority of short-patch base excision repair events are completed by the DNA ligase III alpha/Xrcc1 complex [10].
• Two forms of DNA ligase III are produced by an alternative splicing mechanism [11].
• These findings indicate that DNA ligase III is involved in essential DNA repair activities required for early embryonic development and therefore cannot be replaced by other DNA ligases [8].
• An XRCC1 protein in which this 20mer was deleted could not maintain normal levels of DNA ligase III-alpha in transfected rodent cells, a phenotype associated with defective repair [5] [12].

Anatomical context of LIG3

• Interestingly, cell lines deficient in either DNA ligase I (46BR.1G1) or DNA ligase III (EM9) are sensitive to simple alkylating agents [10].
• In contrast, DNA ligase III-beta, which does not interact with XRCC1, is only expressed in male meiotic germ cells, suggesting a role for this isoform in meiotic recombination [11].
• We have recently purified DNA ligase II and DNA ligase III to near homogeneity from bovine liver and testis tissue, respectively [2].
• In contrast, elevated levels of DNA ligase III mRNA were observed in primary spermatocytes undergoing recombination prior to the first meiotic division [2].
• During male germ cell differentiation, elevated expression of DNA ligase III-beta mRNA is restricted, beginning only in the latter stages of meiotic prophase and ending in the round spermatid stage [13].

Associations of LIG3 with chemical compounds

• The copurification of DNA ligase III activity with histidine-tagged XRCC1 suggests that the two proteins are present in the cell as a complex [14].
• An XRCC1 protein in which the conserved D-block tryptophan was disrupted by point mutation retained the ability to interact with DNA ligase III-alpha, so this tryptophan must mediate a different, although conserved, role [12].
• The degradation of DNA ligase III was prevented by pretreatment with calpeptin, which protected irradiated cells from death [4].
• Calpain binds to the N-terminal region of DNA ligase III, which contains an acidic proline, aspartate, serine, and threonine (PEST) domain frequently present in proteins cleaved by calpain [4].
• Tg does not affect 5'-sugar phosphate removal by the 2-deoxyribose-5-phosphate (dRP) lyase activity of DNA polymerase beta, but further processing of the strand break by purified DNA ligase III was slightly diminished [15].

Physical interactions of LIG3

• In somatic cells, DNA ligase III alpha forms a stable complex with the DNA repair protein Xrcc1 [10].
• These data describe a cell cycle-specific role for a BRCT domain, and we conclude that the XRCC1-DNA ligase III complex is required for DNA strand break repair in G(1) phase of the cell cycle but is dispensable for this process in S phase [16].
• DNA ligase III is recruited to DNA strand breaks by a zinc finger motif homologous to that of poly(ADP-ribose) polymerase. Identification of two functionally distinct DNA binding regions within DNA ligase III [17].

Regulatory relationships of LIG3

• XRCC1 in which the weakly conserved C-block was mutated lost the ability to interact with DNA ligase III-alpha [12].
• HT1080 clones expressing a modified DNA ligase III that lacked a recognizable PEST domain were significantly more resistant to killing by gamma-radiation or 9- amino camptothecin than were cells that overexpressed the wild-type form of DNA ligase III [4].

Other interactions of LIG3

• Three mammalian genes encoding DNA ligases, LIG1, LIG3 and LIG4, have been identified [11].
• DNA ligase II appears to be a proteolytic fragment of DNA ligase III alpha [18].
• Furthermore, DNA ligase III activity was present at lower levels in EM9 cells than in AA8 cells and was returned to normal levels in EM9 cells transfected with pcD2EHX or pcD2EX [14].
• BRCT domains are present in the tumour suppressor protein BRCA1 [1-3], and the domain is found in over 40 other proteins, defining a superfamily that includes DNA ligase III-alpha and the essential human DNA repair protein XRCC1 [12].
• XRCC1-His interacted equally well with DNA ligase III from Bloom syndrome, HeLa and MRC5 cells, indicating that Bloom syndrome DNA ligase III is normal in this respect [19].

Analytical, diagnostic and therapeutic context of LIG3

• Affinity chromatography of extract from EM9 cells transfected with pcD2EHX resulted in the copurification of histidine-tagged XRCC1 and DNA ligase III activity [14].
• Molecular cloning and expression of human cDNAs encoding a novel DNA ligase IV and DNA ligase III, an enzyme active in DNA repair and recombination [20].
• Immunoblotting data suggest that the XRCC1 gene does not code for DNA ligase III [21].
• Third, a series of hemagglutinin-DNA ligase III minigene constructs were introduced into Cos-1 cells, and immunocytochemistry was used to determine subcellular localization of the epitope-tagged DNA ligase III protein [22].
• Full complementation of the ligation defect in EM-C11 extracts was achieved by addition to the repair reaction of recombinant human DNA ligase III but not by XRCC1 [23].

References