DNA ligases catalyse the crucial step of joining the breaks in duplex DNA during DNA replication, repair and recombination, utilising either ATP or NAD(+) as a cofactor [1]. This domain is the catalytic adenylation domain. The NAD+ group is covalently attached to this domain at the lysine in the KXDG motif of this domain. This enzyme- adenylate intermediate is an important feature of the proposed catalytic mechanism [1].

1: Crystal structure of NAD(+)-dependent DNA ligase: modular architecture and functional implications. Lee JY, Chang C, Song HK, Moon J, Yang JK, Kim HK, Kwon ST, Suh SW; EMBO J 2000;19:1119-1129. PMID:10698952

2: Mutational analyses of Aquifex pyrophilus DNA ligase define essential domains for self-adenylation and DNA binding activity. Lim JH, Choi J, Kim W, Ahn BY, Han YS; Arch Biochem Biophys 2001;388:253-260. PMID:11368162

3: Structure of the adenylation domain of an NAD+-dependent DNA ligase. Singleton MR, Hakansson K, Timson DJ, Wigley DB; Structure Fold Des 1999;7:35-42. PMID:10368271