The ubiquitin (Ub) pathway involves three sequential enzymatic steps that facilitate the conjugation of Ub and Ub-like molecules to specific protein substrates. A wide range of enzymes facilitate the proteolytic Ub pathway, including USPs (ubiquitin specific peptidases), which are cysteine proteases that are responsible for the release of ubiquitin from a ubiquitylated substrate and precursor fusion proteins. USP45 (Ubiquitin carboxyl-terminal hydrolase 45), also known as Deubiquitinating enzyme 45, is a 819 amino acid protein that is involved in ubiquitin-dependent protein catabolism. USP45 differs from other USPs in that it contains a UBP-type zinc finger, a domain which binds ubiquitin. Although USP45 is broadly expressed, the highest levels can be found in skeletal muscle, spleen and ovary. There are three isoforms of USP45 which are produced as a result of alternative splicing.