DNA ligase

DNA ligases splint together strands of DNA by ligating (bonding) the 3'-OH and 5'-phosphate terminals of DNA.

DNA ligases functions in both DNA repair and replication replication. DNA ligases are employed as a research tool in recombination experiments in which the ligases are used with restriction enzymes to insert DNA fragments, often genes, into plasmids.

There are four DNA ligases in mammals:
DNA ligase I: ligates some recombinant fragments, and ligates Okazaki fragments during lagging lagging strand DNA replication
DNA ligase II: is an alternatively spliced form of DNA ligase III found in non-dividing cells
DNA ligase III: forms complexes with the DNA repair protein XRCC1 in ligating base excision mutations and recombinant fragments.
DNA ligase IV: forms complexes with XRCC4. It catalyzes the final step in the non-homologous end joining DNA double-strand break repair pathway, and is also operative in V(D)J recombination, the process that generates diversity in immunoglobulin and T-cell receptor loci during development of the immune system.