FIG. 1.

Model for the role of Wss1 in proteasomal degradation of polysumoylated proteins. The Slx5-Slx8 ubiquitin (Ub) ligase conjugates mono-Ub either to the terminal SUMO moiety of polysumoylated protein (left) (7) or directly to the target protein (right). Additional Ub molecules might be added to form a poly-Ub chain in vivo, although in vitro assays showed that only a single Ub was added to the poly-SUMO chain (7). In the model, Wss1 associates with the proteasome and binds to the SUMO moieties of Slx5-Slx8 substrates. The latter interaction stimulates Wss1-dependent cleavage of Ub from the substrate. Wss1 may also help recycle SUMO from the conjugates.