Ubiquitin Specific Peptidase 44 (USP44)

USP44 is not required for the initial recognition of unattached kinetochores and the subsequent recruitment of checkpoint components. Instead, it prevents the premature activation of the anaphase-promoting complex (APC) by stabilizing the APC-inhibitory Mad2-Cdc20 complex. USP44 deubiquitinates the APC coactivator Cdc20 both in vitro and in vivo, and thereby directly counteracts the APC-driven disassembly of Mad2-Cdc20 complexes. The deduced protein has an N-terminal zinc finger ubiquitin-binding (ZNF-UBP) domain, followed by a catalytic domain containing the cys box, QQD box, and his box characteristic of USP enzymes. Northern blot analysis detected a 4.4-kb transcript that was highly expressed in testis, but not in any other tissue examined.