Ubiquitin-binding protein. Required for the progression of DNA replication forks by targeting DNA replication licensing factor CDT1 for degradation. Potentiates but cannot initiate FAS-induced apoptosis. Interacts with CDT1 and ATPase VCP/p97. Interacts (via UBA domain) with FAS (via death domain). Interacts (via UBA domain) with NLRP12 (via DAPIN/PYRIN domain). Central nervous system.