KU PROTEIN STIMULATES DNA END JOINING BY MAMMALIAN DNA LIGASES - A DIRECT ROLE FOR KU IN REPAIR OF DNA DOUBLE-STRAND BREAKS

Ku protein binds to DNA ends and is a cofactor for the DNA-dependent p rotein kinase, Both of these components are involved in DNA double-str and break repair, but it has not been clear if they function indirectl y, by sensing DNA damage and activating other factors, or if they are more directly involved in the processing and rejoining of DNA breaks, We demonstrate that intermolecular ligation of DNA fragments is highly dependent on Ku under conditions designed to mimic those existing in the cell. This effect of Ku is specific to eukaryotic DNA ligases, Ku protein, therefore, has an activity consistent with a direct role in r ejoining DNA breaks and independent of DNA-dependent protein kinase.