InterPro domain: IPR036599

DNA ligase (polydeoxyribonucleotide synthase) is the enzyme that joins two DNA fragments by catalysing the formation of an internucleotide ester bond between phosphate and deoxyribose. It is active during DNA replication, DNA repair and DNA recombination. There are two forms of DNA ligase, one requires ATP ( 6.5.1.1 ), the other NAD ( 6.5.1.2 ), the latter being restricted to eubacteria. Eukaryotic, archaebacterial, viral and some eubacterial DNA ligases are ATP-dependent. The first step in the ligation reaction is the formation of a covalent enzyme-AMP complex. The co-factor ATP is cleaved to pyrophosphate and AMP, with the AMP being covalently joined to a highly conserved lysine residue in the active site of the ligase. The activated AMP residue is then transferred to the 5'phosphate of the nick, before the nick is sealed by phosphodiester-bond formation and AMP elimination [ 1 , 2 ].

This domain superfamily is found in many but not all ATP-dependent DNA ligase enzymes ( 6.5.1.1 ). It is thought to be involved in DNA binding and in catalysis. In human DNA ligase I ( P18858 ), and in Saccharomyces cerevisiae (Baker's yeast) ( P04819 ), this region was necessary for catalysis, and separated from the amino terminus by targeting elements. In Vaccinia virus ( P16272 ) this region was not essential for catalysis, but deletion decreases the affinity for nicked DNA and decreased the rate of strand joining at a step subsequent to enzyme-adenylate formation [ 3 ].

1. Location of the active site for enzyme-adenylate formation in DNA ligases. Proc. Natl. Acad. Sci. U.S.A. 88, 400-4
2. Mammalian DNA ligases. Annu. Rev. Biochem. 61, 251-81
3. Domain structure of vaccinia DNA ligase. Nucleic Acids Res. 25, 727-34