Poly(ADP)-ribosylation (PARylation) regulates chromatin structure and recruits DNA repair proteins. Using single-molecule fluorescence microscopy to track topoisomerase I (TOP1) in live cells, we found that sustained PARylation blocked the repair of TOP1 DNA-protein crosslinks (TOP1-DPCs) in a similar fashion as inhibition of the ubiquitin-proteasome system (UPS). PARylation of TOP1-DPC was readily revealed by inhibiting poly(ADP-ribose) glycohydrolase (PARG), indicating the otherwise transient and reversible PARylation of the DPCs. As the UPS is a key repair mechanism for TOP1-DPCs, we investigated the impact of TOP1-DPC PARylation on the proteasome and found that the proteasome is unable to associate with and digest PARylated TOP1-DPCs. In addition, PARylation recruits the deubiquitylating enzyme USP7 to reverse the ubiquitylation of PARylated TOP1-DPCs. Our work identifies PARG as repair factor for TOP1-DPCs by enabling the proteasomal digestion of TOP1-DPCs. It also suggests the potential regulatory role of PARylation for the repair of a broad range of DPCs.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8373905PMC
http://dx.doi.org/10.1038/s41467-021-25252-9DOI Listing

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