It functions with a cofactor protein,USP1-associated factor 1 (UAF1), that stimulates enzymatic activityand assists substrate engagement.1−3 These substrates includethe DNA clamps—proliferating cell nuclear antigen (PCNA) andFANCI-FANCD2, involved in translesion synthesis4,5 andthe Fanconi Anemia pathway,6−10 respectively. The gene discussed is PCNA; the disease is Fanconi anemia.