Regulator of deubiquitinating complexes, which acts as a strong activator of USP1, USP12 and USP46. Enhances the USP1-mediated deubiquitination of FANCD2; USP1 being almost inactive by itself. Activates deubiquitination by increasing the catalytic turnover without increasing the affinity of deubiquitinating enzymes for the substrate. Also activates deubiquitinating activity of complexes containing USP12. Docks at the distal end of the USP12 fingers domain and induces a cascade of structural changes leading to the activation of the enzyme. Together with RAD51AP1, promotes DNA repair by stimulating RAD51-mediated homologous recombination. Binds single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). 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.Together with ATAD5 and by regulating USP1 activity, has a role in PCNA-mediated translesion synthesis (TLS) by deubiquitinating monoubiquitinated PCNA. Together with ATAD5, has a role in recruiting RAD51 to stalled forks during replication stress. Interacts with USP46. Interacts with USP1. Interacts with USP12. Component of the USP12-WDR20-WDR48 deubiquitinating complex. Interacts with PHLPP1. Interacts with RAD51AP1; the interaction is direct and promotes formation of a trimeric complex with RAD51 via RAD51AP1. Interacts with ATAD5; the interaction regulates USP1-mediated PCNA deubiquitination. Interacts with RAD51; the interaction is enhanced under replication stress. Mainly in cytoplasmic compartments. The WD repeats are required for the interaction with deubiquitinating enzymes USP1, USP12 and USP46. Belongs to the WD repeat WDR48 family.