Atypical E3 ubiquitin-protein ligase, which catalyzes ubiquitination of target proteins together with ubiquitin-conjugating enzyme E2 Ubc10 (PubMed:10880484, PubMed:21900267, PubMed:29689197). Controls the subcellular localization and morphology of muscle nuclei (myonuclei) by regulating the protein levels and distribution of the LINC (LInker of Nucleoskeleton and Cytoskeleton) complex (PubMed:29689197). Functions by mediating the monoubiquitination of the LINC complex subunit koi leading to its subsequent proteasomal degradation (PubMed:29689197). Appears to function, at least partially redundantly, with the RBR E3 ligase family member park in nuclear localization and morphology (PubMed:29689197). Likely to function in metamorphosis by regulating the proteins levels of EcR isoform A (ECR-A) and its heterodimeric partner usp, via the ubiquitination and subsequent degradation of ECR-A (PubMed:21900267). [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. Can form homodimers (PubMed:10880484, PubMed:29689197). Interacts (via RING-type 1 zinc finger) with Ubc10 (PubMed:10880484, PubMed:29689197). Interacts with the LINC complex member koi (PubMed:29689197). Interacts with park (PubMed:29689197). Interacts with ari-2 (PubMed:29689197). Specifically interacts with isoform ECR-A of EcR (PubMed:21900267). Mainly cytoplasmic. Widely expressed, with prominent levels in the nervous system and female gonads. Expressed in all tissues throughout development, with maximum levels reached during metamorphosis and maintained in the adult. Members of the RBR family are atypical E3 ligases. They interact with E2 conjugating enzymes such as Ubc10 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. Autophosphorylated. Pharate pupae lethal. Larval muscles exhibit an increase in nuclear clustering. Belongs to the RBR family. Ariadne subfamily.