A diverse set of additional molecular partners, each associating specifically with a selective domain of RanBP2, are likely to impart and integrate additional roles to RanBP2. For example, the cyclophilin-like domain (CLD), the internal repeat (W1W2/IR), and zinc-finger rich (ZnF) domains of RanBP2 associate specifically with components of the 19S cap of the proteasome [14], the E2 SUMO-1-conjugating enzyme (Ubc9) [15], and the nuclear export receptor, CRM1/exportin-1 [16], respectively. RanBP2 itself was also found to exhibit SUMO1 E3 ligase activity [17], supporting a direct link between RanBP2-mediated SUMO-1 substrate modification and relocation of SUMO-1 modified cytosolic substrates (e.g., RanGAP) to the cytosolic face of the nuclear pore complex (NPC) [18]. Finally, RanBP2 was also found to localize prominently to the mitochondria-rich ellipsoid subcellular compartment of photosensory neurons [19] and to RanGTPase-restricted foci along cytoplasmic tracks [19], in addition to its localization at cytoplasmic fibrils emanating from nuclear pores [2,3,10,12,19].