Electron microscopy visualization of DNA-protein complexes formed by Ku and DNA ligase IV

► To resolve DSBs DNA ends are brought together by protein complexes. ► Ku heterodimers recognize specifically DNA ends as shown by EM. ► Ku alone is not sufficient for DNA end bridging but requires Dnl4/Lif1 (Ligase IV/XRCC4). ► Ligase IV mediates end-bridging by bringing two Ku-bound DNA ends.