Ubiquitin (Ub) is a highly conserved protein found ubiquitously in eukaryotic organisms. The conjugation of ubiquitin to proteins is an important means to regulate protein activity for many cellular processes by tagging them for degradation. Removal of Ub can rescue proteins from degradation. This is accomplished by the ubiquitin-specific processing protease (UBP) family of enzymes. Ubiquitin specific processing protease 1 (USP1) has been found to play a role in the Fanconi anemia DNA repair pathway. USP1 specifically removes monoubiquitination from the Fanconi anemia D2 (FANCD2) protein and from the proliferating cell nuclear antigen (PCNA). Deubiquitination of FANCD2 and PCNA is critical to their role in the DNA damage response and DNA crosslink repair.