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Domain Structure of a NHEJ DNA Repair Ligase from Mycobacterium tuberculosis
A prokaryotic non-homologous end-joining (NHEJ) system for the repair of DNA double-strand breaks (DSBs), composed of a Ku homodimer (Mt-Ku) and a multidomain multifunctional ATP-dependent DNA ligase (Mt-Lig), has been described recently in Mycobacterium tuberculosis. Mt-Lig exhibits polymerase and...
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Published in: | Journal of molecular biology 2005-08, Vol.351 (3), p.531-544 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | A prokaryotic non-homologous end-joining (NHEJ) system for the repair of DNA double-strand breaks (DSBs), composed of a Ku homodimer (Mt-Ku) and a multidomain multifunctional ATP-dependent DNA ligase (Mt-Lig), has been described recently in
Mycobacterium tuberculosis. Mt-Lig exhibits polymerase and nuclease activity in addition to DNA ligation activity. These functions were ascribed to putative polymerase, nuclease and ligase domains that together constitute a monomeric protein. Here, the separate polymerase, nuclease and ligase domains of Mt-Lig were cloned individually, over-expressed and the soluble proteins purified to homogeneity. The polymerase domain demonstrated DNA-dependent RNA primase activity, catalysing the synthesis of unprimed oligoribonucleotides on single-stranded DNA templates. The polymerase domain can also extend DNA in a template-dependent manner. This activity was eliminated when the catalytic aspartate residues were replaced with alanine. The ligase domain catalysed the sealing of nicked double-stranded DNA designed to mimic a DSB, consistent with the role of Mt-Lig in NHEJ. Deletion of the active-site lysine residue prevented the formation of an adenylated ligase complex and consequently thwarted ligation. The nuclease domain did not function independently as a 3′-5′ exonuclease. DNA-binding assays revealed that both the polymerase and ligase domains bind DNA
in vitro, the latter with considerably higher affinity. Mt-Ku directly stimulated the polymerase and nuclease activities of Mt-Lig. The polymerase domain bound Mt-Ku
in vitro, suggesting it may recruit Mt-Lig to Ku-bound DNA
in vivo. Consistent with these data, Mt-Ku stimulated the primer extension activity of the polymerase domain, suggestive of a functional interaction relevant to NHEJ-mediated DSB repair processes. |
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ISSN: | 0022-2836 1089-8638 |
DOI: | 10.1016/j.jmb.2005.06.038 |