Molecular triage and isoform protection safeguard ubiquitin chain editing on DNA.

Ubiquitin-dependent fate control and isoform diversity safeguard ZUP1, a key ubiquitin chain-editing enzyme, maintaining RPA turnover on ssDNA in cells.

• Why it matters: Maintaining a functional RPA-ZUP1 pool is crucial to prevent pathological RPA trapping on ssDNA, which can impair DNA repair processes. Understanding how ZUP1 homeostasis is regulated addresses a gap in knowledge about DNA damage response regulation.
• What they did: The study investigates ZUP1 regulation through ubiquitination, recruitment of p97/VCP and ATXN3, and the roles of E3 ligases UBR5 and HUWE1, along with the identification of a naturally occurring ZUP1 isoform resistant to ubiquitination.
• The result: Findings reveal a molecular triage pathway that protects ZUP1 from premature degradation and suggest that isoform diversity provides a protected pool of chain-editing activity, enabling homeostasis on damaged chromatin.