Lesion recognition by XPC is PARP dependent. (A and B) Cells stably expressing XPC-GFP (XP4PA) were DMSO treated or PARP inhibitor (PARPi) treated and subjected to Strip-FRAP analysis, as indicated. Quantitative analysis of the mobility of XPC-GFP in unchallenged cells that were treated with DMSO or PARP inhibitor (A) or XPC-GFP in UV-C–irradiated (8 J/m²) cells that were treated with DMSO or PARP inhibitor (B) is shown. Values represent the mean of ∼20 cells. (C) Western blot (WB) of high–molecular mass PAR chains after transfection with siRNAs targeting luciferase (siLuc) or PARG (siPARG) in U2OS cells. Histone H2B serves as a loading control. (D) U2OS cells were treated with DMSO or PARP inhibitor, locally UV irradiated (10 J/m² through 8-µm pores), and subsequently stained for endogenous XPC (green) and CPDs (red). (E) U2OS cells were transfected with siLUC or siPARG, locally UV irradiated (10 J/m² through 8-µm pores), and subsequently stained for endogenous XPC (green) and CPDs (red). (F and G) The quantification of the relative accumulation of XPC (red bars) or the enrichment of CPDs (blue bars) is shown in F (10 J/m²) and G (25 J/m²). The signal represents the relative increase at the locally damaged site relative to the signal in the nondamaged nuclear region (∼50 cells for each condition collected in two independent experiments). Accumulation of XPC is normalized to 1 for comparison. So, DMSO is set to 1 (and PARPi expressed relative to this value), and siLUC is set to 1 (and siPARG expressed relative to this value). Error bars represent the SD.