Ubiquitin Specific Peptidase 3 (USP3)

Ubiquitin is a highly conserved 76-amino acid protein involved in the regulation of intracellular protein breakdown, cell cycle regulation, and stress response. Ubiquitin is released from degraded proteins by disassembly of the polyubiquitin chains, which is mediated by ubiquitin-specific proteases .By searching an EST database for USP-like sequences and screening a testis cDNA library, Sloper-Mould et al. (1999) identified a cDNA encoding a deduced 521-amino acid protein termed USP3. Southern blot analysis showed that USP3 is a single-copy gene. Northern blot analysis detected expression of a major 2.5- and a minor 5.8-kb USP3 transcript in all tissues examined, with strongest expression in pancreas. Functional analysis demonstrated that USP3 cleaves ubiquitin in vitro and, like USP4, efficiently does so at ubiquitin-proline bonds.