LigD

{{Infobox nonhuman protein

|Name=Multifunctional non-homologous end joining protein LigD

|Symbol=ligD

|Organism=Mycolicibacterium smegmatis ATCC 700084

|UniProt=A0R3R7

}}

LigD is a multifunctional ligase/polymerase/nuclease (3'-phosphoesterase) found in bacterial non-homologous end joining (NHEJ) DNA repair systems.{{cite journal |vauthors=Della M, Palmbos PL, Tseng HM, etal |title=Mycobacterial Ku and ligase proteins constitute a two-component NHEJ repair machine |journal=Science |volume=306 |issue=5696 |pages=683–5 |date=October 2004 |pmid=15499016 |doi=10.1126/science.1099824 |bibcode=2004Sci...306..683D |s2cid=38823696 }} It is much more error-prone than the more complex eukaryotic system of NHEJ, which uses multiple enzymes to fill its role.{{cite journal |vauthors=Gong C, Bongiorno P, Martins A, etal |title=Mechanism of nonhomologous end-joining in mycobacteria: a low-fidelity repair system driven by Ku, ligase D and ligase C |journal=Nat. Struct. Mol. Biol. |volume=12 |issue=4 |pages=304–12 |date=April 2005 |pmid=15778718 |doi=10.1038/nsmb915 |s2cid=6879518 }} The polymerase preferentially use rNTPs (RNA nucleotides), possibly advantageous in dormant cells.{{cite journal |vauthors=Pitcher RS, Green AJ, Brzostek A, Korycka-Machala M, Dziadek J, Doherty AJ |title=NHEJ protects mycobacteria in stationary phase against the harmful effects of desiccation |journal=DNA Repair (Amst.) |volume=6 |issue=9 |pages=1271–6 |date=September 2007 |pmid=17360246 |doi=10.1016/j.dnarep.2007.02.009 |url=http://sro.sussex.ac.uk/1122/1/DNA_Doherty.pdf}}

The actual architecture of LigD is variable.

• The LigD homolog in Bacillus subtilis does not have the nuclease domain.
• LigD with its ligase domain artificially removed can perform its function (with loss of fidelity) with a separate LigC acting as the ligase.
• The LigD homolog in the archaeon Methanocella paludicola is broken into three single-domain proteins sharing an operon.{{cite journal |last1=Bartlett |first1=EJ |last2=Brissett |first2=NC |last3=Doherty |first3=AJ |title=Ribonucleolytic resection is required for repair of strand displaced nonhomologous end-joining intermediates. |journal=Proceedings of the National Academy of Sciences of the United States of America |date=28 May 2013 |volume=110 |issue=22 |pages=E1984-91 |doi=10.1073/pnas.1302616110|pmc=3670387 |pmid=23671117 |bibcode=2013PNAS..110E1984B |doi-access=free}}