USP19 is a deubiquitinating enzyme with a preference towards Lys-63-linked ubiquitin chains (Iphofer et al. 2012). It deubiquitinates RNF123, preventing its proteasomal degradation which in turn stimulates CDKN1B ubiquitin-dependent degradation and thereby cell proliferation (Lu et al. 2009).
thiol-dependent deubiquitinase activity of USP19:K63polyUb-RNF123 [cytosol]