 This study examined the behavior of DNA repair factors in living cells using single molecule imaging techniques. The researchers found that the shielding complex, a key component of n-joining, did not form a pre-assembled structure but rather accumulated at DNA breaks over time. They also observed that the MDC1 protein interacted with chromatin through its PST repeat domain, suggesting that this interaction may be important for DNA repair. These findings provide valuable insight into the mechanisms behind DNA repair and could help inform future treatments for diseases caused by defective DNA repair. This article was authored by Joshua Arhazer, Maria Mikova, Oslo Bowl, and others.