The ubiquitin-dependent protein degradation pathway is essential for proteolysis of intracellular proteins and peptides. Enzymes that remove ubiquitin from ubiquitin-conjugated peptides, like USP28, affect the fate and degradation of intracellular proteins and are essential for maintenance of cell-free ubiquitin pools (Valero et al., 2001).[supplied by OMIM, Mar 2008]