C) Comparison of USP1DM1, USP1PIP1 and USP1PIP1+DM1 (+UAF1) activity on DNA-loaded PCNA-Ub (solid lines) and free PCNA-Ub (dashed lines) shows reduced increase in activity of these mutants compared to USP1WT. Left panel: Quantification of gel based activity assays showing percentage of cleaved PCNA-Ub at the mentioned time points (n=2, technical replicates), Right panel: Quantification of the activation fold observed in USP1WT, USP1PIP1, USP1DM1 and USP1PIP1+DM1 on DNA-loaded PCNA-Ub versus free PCNA-Ub (n=2, technical replicates). 