Inhibition of UVSSA ubiquitination suppresses transcription-coupled nucleotide excision repair deficiency caused by dissociation from USP7.

Transcription-coupled nucleotide excision repair (TC-NER) is a subpathway of nucleotide excision repair that efficiently removes transcription-blocking DNA damage from the transcribed strands of active genes. UVSSA is a causative gene for UV-sensitive syndrome (UV^S S), which is an autosomal recessive disorder characterized by hypersensitivity to UV light and deficiency in TC-NER. UV-stimulated scaffold protein A (UVSSA), the product of UVSSA, forms a complex with ubiquitin-specific peptidase 7 (USP7) and is stabilized by interaction with USP7. The central region of UVSSA, which contains the tumor necrosis factor receptor-associated factor (TRAF)-binding motif, is required for the interaction with the N-terminal TRAF domain of USP7. Here, we showed that UVSSA is mono-ubiquitinated in vitro and identified a lysine residue (Lys⁴¹⁴ ) in UVSSA as the target of ubiquitination. The deubiquitination activity of USP7 was inhibited by the ubiquitin-conjugating enzyme UbcH6. Lys⁴¹⁴ was also modified by poly-ubiquitin chains in vivo. UVSSA deficient in the interaction with USP7 is ubiquitinated and degraded by the proteasome, and the degradation leads to deficiency in TC-NER. The substitution of Lys⁴¹⁴ by Arg of UVSSA inhibited its degradation and thereby suppressed the deficiency in TC-NER.

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