Figure 1. Schematic diagram of KAP1 phosphorylation and dephosphorylation. ATM-mediated phosphorylation of KAP1 on serine 824 leads to transient relaxation of chromatin allowing double-strand break repair processes to operate more easily within inactive chromatin domains. KAP1 phosphorylation is reversed by the PP4 phosphatase complex before completion of the repair process.