Ubiquitin-binding protein (PubMed:19722279). Required for the progression of DNA replication forks by targeting DNA replication licensing factor CDT1 for degradation (PubMed:26842564). Potentiates but cannot initiate FAS-induced apoptosis (By similarity). {ECO:0000250|UniProtKB:P54731, ECO:0000269|PubMed:19722279, ECO:0000269|PubMed:26842564}. This is the function of Ensembl gene identifier ENSG00000185104 (FAF1, Fas associated factor 1).