 Upon generation of a DSB, Ku proteins will move through the cytoplasm until they find the site of the break and bind to it.Ku recruits XRCC4 and Cer-XLF and both of these proteins interact cooperatively with one another through specific residues to form a nucleoprotein pore complex that wraps around DNA.Cer-XLF is a homodimer that is very similar to XRCC4 in the structure and size of its N-terminal and C-terminal domains.