Of the all known mammalian DNA ligases, only Lig III has been found to be present in mitochondria. DNA ligase IV: complexes with XRCC4. It catalyzes the final step in the non-homologous end joining DNA double-strand break repair pathway.

What does a ligase do?

Ligases are enzymes that are capable of catalyzing the reaction of joining two large molecules by establishing a new chemical bond, generally with concomitant hydrolysis of a small chemical group on one of the bulky molecules or simply linking of two compounds together (e.g., enzymes that catalyze joining of C–O, C–S, ...

Where is the ligase in DNA replication?

On the leading strand, DNA synthesis occurs continuously. On the lagging strand, DNA synthesis restarts many times as the helix unwinds, resulting in many short fragments called “Okazaki fragments.” DNA ligase joins the Okazaki fragments together into a single DNA molecule.