Enables ubiquitin protein ligase activity. Acts upstream of or within several processes, including negative regulation of macromolecule metabolic process; regulation of signal transduction; and regulation of vesicle-mediated transport. Located in vesicle. Is expressed in genitourinary system; hippocampus; and retina nuclear layer. Orthologous to human RABGEF1 (RAB guanine nucleotide exchange factor 1). [provided by Alliance of Genome Resources, Apr 2022]