To identify factors that limit the DNA-damage-induced histone ubiquitylation, we cultured U-2-OS cells stably expressing green fluorescent protein (GFP)-RNF168 on small interfering RNA (siRNA) arrays targeting the known human ubiquitinome, and we screened for genes whose knockdown by at least two independent siRNAs increased GFP-RNF168 accumulation on the G1 nuclear bodies formed around spontaneous DNA lesions