DUBs of the Ub C-terminal Hydrolase (UCH) family are thiol proteases that have an N-terminal catalytic domain sometimes followed by C-terminal extensions that mediate protein-protein interactions. Humans have four UCH DUBs (UCH-L1, UCH-L3, UCH37/UCH-L5, and BAP1) that can be divided into the smaller UCH DUBs (UCH-L1 and UCH-L3), which cleave small leaving groups from the C-terminus of ubiquitin (Larsen et al. 1998), and the larger UCH DUBs (UCH37 and BAP1), which can disassemble poly-Ub chains (Misaghi et al. 2009, Lam et al. 1997).