The enzyme, typically found in bacteria, catalyses the ligation of DNA strands with 3'-hydroxyl and 5'-phosphate termini, forming a phosphodiester and sealing certain types of single-strand breaks in duplex DNA. Catalysis occurs by a three-step mechanism, starting with the activation of the enzyme by NAD+, forming a phosphoramide bond between adenylate and a lysine residue. The adenylate group is then transferred to the 5'-phosphate terminus of the substrate, forming the capped structure 5'-(5'-diphosphoadenosine)-[DNA]. Finally, the enzyme catalyses a nucleophilic attack of the 3'-OH terminus on the capped terminus, which results in formation of the phosphodiester bond and release of the adenylate. RNA can also act as substrate, to some extent. cf. EC 188.8.131.52
, DNA ligase (ATP), EC 184.108.40.206
, DNA ligase (ATP or NAD+), and EC 220.127.116.11
, DNA ligase (ATP, ADP or GTP).