DNA ligase 4 (LIG4)

Efficiently joins single-strand fractures in a double- stranded polydeoxynucleotide in an ATP-dependent reaction. Involved in DNA non-homologous end joining (NHEJ) required for double-strand break repair and V(D)J recombination.

The LIG4-XRCC4 complex accounts for the NHEJ ligation step, and XRCC4 enhances the linking activity of LIG4. Binding of the LIG4-XRCC4 complex to DNA ends is determined by the assembly of the DNA- dependent protein kinase complex DNA-PK to these DNA ends.