sentences:  The function of these modifications is still unknown, but it has been proposed that ADP-ribosylation modulates higher-order chromatin structure in efforts to facilitate more accessible sites for repair factors to migrate to the DNA damage.The ubiquitin-proteasome system (UPS) figures prominently in protein degradation.The 26S proteasome consists of a catalytic subunit (the 20S core particle), and a regulatory subunit (the 19S cap).