Mediates ubiquitination and subsequent desumoylation/degradation of sumoylated proteins and proteins containing SUMO-like domains. Involved in maintaining genome stability where it acts in the cellular response to DNA damage. Has a role in meiosis. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Part of an E3 ubiquitin complex including rfp1, rfp2 and slx8. Interacts with slx8, chk1, nse5, pmt3 and rad60.