Hydrolase that deubiquitinates polyubiquitinated target proteins (PubMed:25027767). Required for preventing the activation of the Toll signaling cascades under unchallenged conditions (PubMed:25027767). Essential for bodily calcium homeostasis (PubMed:26756164). Required for preventing the activation of the immune deficiency (Imd) signaling cascade under unchallenged conditions. Regulates the Imd pathway by specifically removing 'Lys-48'-linked ubiquitin from imd. Also promotes imd degradation probably by binding to imd and enhancing its association with the proteasome. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Interacts (via N-terminus) with imd (via N-terminus). Interacts with Rpt6. RNAi-mediated knockdown is pupal lethal (PubMed:24026097, PubMed:26756164). Pharate adults removed from their pupal cases display severe defects in head eversion, with head structures forming within the thoracic area (PubMed:24026097). Pupal lethality can be rescued by supplementing their diet with CaCl2 (PubMed:26756164). RNAi-mediated knockdown in the fat body results in the activation of the Imd and Toll signaling pathways under unchallenged conditions, with constitutive expression of the Toll (Drs, IM1) and Imd (DptA, Def, Atta) antimicrobial peptides (PubMed:25027767). Flies infected with E.coli display enhanced expression of Atta and DptA compared to controls (PubMed:25027767). Double knockdown with imd prevents the enhanced expression of Atta and DptA in uninfected and infected flies (PubMed:25027767). RNAi-mediated knockdown in the clock neurons (tim) does not affect the free-running period of circadian rhythms under light-dark (LD) and constant dark (DD) conditions (PubMed:26756164). Belongs to the peptidase C19 family.