The RPA complex orchestrates K63-linked deubiquitination via ZUP1

Ubiquitin signaling is regulated by deubiquitinating enzymes (DUBs), which can edit or remove ubiquitin from substrates. Recently, ZUP1 was discovered as the founding and only member of a novel DUB class that cleaves long K63-linked ubiquitin chains, with a putative role in DNA repair. However, ZUP1 has poor activity on its own, suggesting additional mechanisms exist to promote its activity in cells. Here, using a range of cellular, biochemical, and structural proteomics approaches, we show that ZUP1 directly interacts with the RPA complex, a single-stranded DNA binding protein complex involved in DNA replication and multiple DNA repair processes. Functionally, the ZUP1-RPA complex interaction dramatically stimulates ZUP1 K63-linked DUB activity, which occurs through S1 and S1' site communication. Collectively, our results suggest a mechanism that couples sensing of ssDNA to the activation of K63-linked deubiquitination via the ZUP1-RPA complex.