Small Ubiquitin-like Modifiers (SUMOs) are a family of small, related proteins that can be enzymatically conjugated to a target protein by a post-translational modification process termed SUMOylation. SUMO-2 is a highly conserved, small ubiquitin-related modifier that has been shown to be covalently conjugated to a large variety of cellular proteins (Dai and Liew, 2001; Kamitani et al., 1997; Su and Li, 2002). Identification and cloning of human SUMO-2 was first described by Kamitani et al. (1997). Mouse and human SUMO-2 proteins are identical, with human SUMO-2 sharing 44% and 86% amino acid identity with SUMO-1 and SUMO-3, respectively (Su and Li, 2002). SUMO-2 has been shown to interact with the E3 ligase RNF28 through its RING domain (Dai and Liew, 2001). SUMO-2 is conjugated to a target protein in a similar way to ubiquitin and has been implicated in multiple cellular processes, including nuclear transport, cell cycle control, oncogenesis, inflammation and response to viral infection. SUMO-2 forms a number of conjugates similar to those of SUMO-1, first requiring cleavage of its C terminus for conjugation to occur (Kamitani et al., 1997). RANGAP1 is modified by either SUMO-2 or SUMO-1, and formation of the sentrinized (SUMOylated) RANGAP1 requires covalent linkage between itself and SUMO-2 or SUMO-1 (Kamitani et al., 1997). SUMO-2 has been localised predominantly to nuclear bodies, distinct from SUMO-1 and SUMO-3 which are found localised to the nuclear membrane (Matunis et al., 1996).
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