Enables ubiquitin protein ligase activity. Acts upstream of or within protein ubiquitination. Located in early endosome. Part of ubiquitin ligase complex. Is expressed in several structures, including 4th ventricle choroid plexus; genitourinary system; gut; hair follicle; and hemolymphoid system gland. Orthologous to human MIB2 (MIB E3 ubiquitin protein ligase 2). [provided by Alliance of Genome Resources, Apr 2022]