Might act as an E3 ubiquitin-protein ligase, or as part of E3 complex, which accepts ubiquitin from specific E2 ubiquitin-conjugating enzymes and then transfers it to substrates. [E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-N(6)-ubiquitinyl-L-lysine. Binds 4 Zn(2+) ions per subunit. Protein modification; protein ubiquitination. Members of the RBR family are atypical E3 ligases. They interact with the E2 conjugating enzyme UBE2L3 and function like HECT-type E3 enzymes: they bind E2s via the first RING-type zinc finger, but require an obligate trans-thiolation step during the ubiquitin transfer, requiring a conserved active site Cys residue in the second RING-type zinc finger. The active site probably forms a thioester intermediate with ubiquitin taken from the active-site cysteine of the E2 before ultimately transferring it to a Lys residue on the substrate. Belongs to the RBR family. Ariadne subfamily. Could be the product of a pseudogene.