Fig. 4.

Ku protein functions in two different ways in dealing with DNA damage. When DNA damage (presumably DSB) occurs, Ku binds at the end of DNA and protects it, and alarms DNA damage checkpoints to protect genome. However, if DNA damage persists, Ku changes its role to recruit other DNA metabolism machinery to generate GCRs. In this stage, Ku might be modified differently compared with when it protects genome through DNA repair, telomere maintenance, and DNA damage checkpoints. Ku might interact with telomerase directly to generate de novo telomere additions or Ku could participate in the production of large deletions or translocations with ligase 4. Stars and crosses represent putative different modifications that might direct divergent roles of Ku.