HR and NHEJ. NHEJ) NHEJ starts with recognition of the DNA ends by the Ku70/80 heterodimer, which recruits DNA-PKcs. If the ends are incompatible, nucleases such as Artemis can trim the ends. The XRCC4-DNA Ligase IV-XLF ligation complex seals the break. HR) The MRN-CtIP-complex starts resection on the breaks to generate single stranded DNA (ssDNA). After resection the break can no longer be repaired by NHEJ. The ssDNA is first coated by RPA, which is subsequently replaced by Rad51 with the help of BRCA2. These Rad51 nucleoprotein filaments mediate strand invasion on the homologous template. Extension of the D-loop and capture of the second end lead to repair.