Ubiquitinating enzymes (UBEs) catalyze protein ubiquitination, a reversible process countered by deubiquitinating enzyme (DUB) action . Five DUB subfamilies are recognized, including the USP, UCH, OTU, MJD and JAMM enzymes. Herpesvirus-associated ubiquitin-specific protease (HAUSP, USP7) is an important deubiquitinase belonging to USP subfamily. A key HAUSP function is to bind and deubiquitinate the p53 transcription factor and an associated regulator protein Mdm2, thereby stabilizing both proteins . In addition to regulating essential components of the p53 pathway, HAUSP also modifies other ubiquitinylated proteins such as members of the FoxO family of forkhead transcription factors and the mitotic stress checkpoint protein CHFR .