Regulator of deubiquitinating complexes, which acts as a strong activator of USP1, USP12 and USP46 (PubMed:18082604, PubMed:19075014, PubMed:26388029, PubMed:31253762). Enhances the USP1- mediated deubiquitination of FANCD2; USP1 being almost inactive by itself (PubMed:18082604, PubMed:31253762). Activates deubiquitination by increasing the catalytic turnover without increasing the affinity of deubiquitinating enzymes for the substrate (PubMed:19075014, PubMed:27373336). Also activates deubiquitinating activity of complexes containing USP12 (PubMed:19075014, PubMed:27373336, PubMed:27650958). In complex with USP12, acts as a potential tumor suppressor by positively regulating PHLPP1 stability (PubMed:24145035). Docks at the distal end of the USP12 fingers domain and induces a cascade of structural changes leading to the activation of the enzyme (PubMed:27373336, PubMed:27650958). Together with RAD51AP1, promotes DNA repair by stimulating RAD51-mediated homologous recombination (PubMed:27239033, PubMed:27463890, PubMed:32350107). Binds single- stranded DNA (ssDNA) and double-stranded DNA (dsDNA) (PubMed:27239033, PubMed:31253762, PubMed:32350107). DNA-binding is required both for USP1-mediated deubiquitination of FANCD2 and stimulation of RAD51- mediated homologous recombination: both WDR48/UAF1 and RAD51AP1 have coordinated role in DNA-binding during these processes (PubMed:31253762, PubMed:32350107). Together with ATAD5 and by regulating USP1 activity, has a role in PCNA-mediated translesion synthesis (TLS) by deubiquitinating monoubiquitinated PCNA (PubMed:20147293). Together with ATAD5, has a role in recruiting RAD51 to stalled forks during replication stress (PubMed:31844045). {ECO:0000269|PubMed:18082604, ECO:0000269|PubMed:19075014, ECO:0000269|PubMed:20147293, ECO:0000269|PubMed:24145035, ECO:0000269|PubMed:26388029, ECO:0000269|PubMed:27239033, ECO:0000269|PubMed:27373336, ECO:0000269|PubMed:27463890, ECO:0000269|PubMed:27650958, ECO:0000269|PubMed:31253762, ECO:0000269|PubMed:31844045, ECO:0000269|PubMed:32350107}. (Microbial infection) In case of infection by Herpesvirus saimiri, may play a role in vesicular transport or membrane fusion events necessary for transport to lysosomes. Induces lysosomal vesicle formation via interaction with Herpesvirus saimiri tyrosine kinase- interacting protein (TIP). Subsequently, TIP recruits tyrosine-protein kinase LCK, resulting in down-regulation of T-cell antigen receptor TCR. May play a role in generation of enlarged endosomal vesicles via interaction with TIP (PubMed:12196293). In case of infection by papillomavirus HPV11, promotes the maintenance of the viral genome via its interaction with HPV11 helicase E1 (PubMed:18032488). . This is the function of Ensembl gene identifier ENSG00000114742 (WDR48, WD repeat domain 48).