SUMOs
The small ubiquitin-like modifiers (SUMOs) are involved in many cellular processes and is required for normal growth and development in all eukaryotes.
Whereas lower eukaryotes have a single version of SUMO, higher eukaryotes have three versions: SUMO1, SUMO2 and SUMO3.
Similarly to most other ubiquitin-like proteins, the primary translation products of the SUMO genes need to be proteolytically processed to expose the C-terminal glycine that will be linked to lysine side chains in substrates.
Processing of SUMO precursors is mediated by SUMO-specific proteases that also remove SUMO from modified proteins and depolymerise poly-SUMO chains.
References
Hay RT. SUMO-specific proteases: a twist in the tail. Trends Cell Biol. 2007 Aug;17(8):370-6. PMID: #17768054#