Fig. 1. Identification of trapped PARP1-interacting proteins.

a, Schematic describing the identification of trapped PARP1 protein–protein interactomes via RIME or proximity labelling linked to mass spectrometry. The cells were exposed to either PARPi + MMS (to enable trapping) or MMS (no trapping) for 1 h, after which PARP1-interacting/proximal proteins were identified by mass spectrometry analysis. BP, biotin-phenol. b, Clonogenic assay illustrating the restoration of PARPi sensitivity in the complemented PARP1^–/– CAL51 cells as described in a. PARP1 protein expression in the different clones is shown in Extended Data Fig. 1a. c, Quantification of the colony formation assay shown in b; data are the mean of two biological replicates. d, PARP1^WT–Apex2–eGFP protein localizes to sites of DNA damage, generates PAR and can be trapped by PARPi. Cells expressing PARP1^WT–Apex2–eGFP were transfected with a PAR sensor, a PBZ PAR-binding domain fused to mRuby2 (left). PARP1^WT–Apex2–eGFP and PBZ–mRuby2 accumulate at the sites of UV micro-irradiation. Exposure to 100 nM talazoparib causes sustained accumulation of PARP1^WT–Apex2–eGFP (middle) but abolishes PAR production (right). Data represent two independent experiments with similar results. DMSO, dimethylsulfoxide. e,f, PARP1 interactions that are enriched under PARP1-trapping conditions (as defined by the PSM ratio ((talazoparib + MMS) ÷ MMS) and MS scores). Scatter plots are shown for PARP1^WT–eGFP (e) and PARP1^{del.p.119K120S}–eGFP (f) RIME. g, PARP1 interactions that are enriched under PARP1-trapping conditions for PARP1^WT–Apex2–eGFP proximity labelling. RIME and proximity labelling were performed in three independent experiments. h, A graph plotting the PSM against MS score for PARP1^WT–Apex2–eGFP proximity labelling interactions shows that p97 is among the most abundant proteins identified in the PARP1^WT–Apex2–eGFP proximity labelling.

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