Ubiquitin Specific Peptidase 18 (USP18)

USP18, a member of the deubiquitinating protease family of enzymes, is thought to remove ISG15 adducts from a broad range of protein substrates. The deduced 372-amino acid protein has a calculated molecular mass of about 43 kD. It contains 6 domains conserved among members of the ubiquitin-binding protein family, including the cys box, which has putative transmembrane helices and a conserved putative active-site cysteine at cys64, and 3 blocks of the his box region. The sequence also contains an amidation site and 2 N-glycosylation sites. USP18 shares 70% sequence identity with mouse Usp18. Northern blot analysis revealed a single transcript of about 1.9-kb in several human cell lines. Fluorescence microscopy demonstrated fluorescence-tagged USP18 within the nucleoplasm of transfected HeLa cells.