SUMO-1 is a small ubiquitin-like protein that can be covalently conjugated to other proteins. A family of proteases catalyzes deconjugation of SUMO-1-containing species. Members of this family also process newly synthesized SUMO-1 into its conjugatable form. To understand these enzymes better, we have examined the localization and behavior of the human SUMO-1 protease SENP2. Here we have shown that SENP2 associates with the nuclear face of nuclear pores and that this association requires protein sequences near the N terminus of SENP2. We have also shown that SENP2 binds to Nup153, a nucleoporin that is localized to the nucleoplasmic face of the pore. Nup153 binding requires the same domain of SENP2 that mediates its targeting in vivo. Removal of the Nup153-interacting region of SENP2 results in a significant change in the spectrum of SUMO-1 conjugates within the cell. Our results suggest that association with the pore plays an important negative role in the regulation of SENP2, perhaps by restricting its activity to a subset of the conjugated proteins within the nucleus.
SUMO-11 is a ubiquitin-like protein that can be covalently conjugated to other proteins through an isopeptide linkage in a manner similar to ubiquitin (1). The SUMO-1 conjugation pathway utilizes proteins that both show sequence similarity to analogous enzymes in the ubiquitin pathway and utilize similar biochemical mechanisms (1). A large and growing number of SUMO-1 conjugation substrates have been reported in vertebrates (1). Notably, the profile of SUMO-1-conjugated proteins changes substantially in response to altered cellular conditions (see Ref. 2), suggesting that there are mechanisms to control the specificity of conjugation and/or deconjugation of SUMO-1 differentially between distinct substrates.Unlike enzymes of the SUMO-1 conjugation pathway, enzymes involved in SUMO processing and deconjugation are not closely related by sequence to their ubiquitin counterparts. Rather, known SUMO proteases share sequence homology in their catalytic domains, which is more nearly conserved to viral proteases (3). Two SUMO proteases have been described in budding yeast, Ulp1p (3) and Ulp2p/Smt4p (4, 5). Ulp1p is concentrated near the nuclear periphery (5) and interacts with nuclear pore components in two-hybrid assays (6), while Ulp2p is localized throughout the nucleus (5). ULP1 is an essential gene, and temperature-sensitive (ts) Ulp1p mutants arrest at the G2/M transition of the cell cycle. Ulp2 is not essential, but it is required for normal meiotic development, for regulation of spindle checkpoint arrest, and for chromatin condensation of rDNA during mitosis (4, 5). Interestingly, these proteins do not appear to act in a simple complementary manner, since ulp1-ts/ulp2-null double mutants grow better than ulp2 single mutants under a variety of conditions (5).In mammals, data base searches find at least seven members of the SUMO protease family (7), some of which have now been confirmed to act as SUMO proteases in vitro (8 -11). Outside of their c...