E3 ubiquitin-protein ligase, which catalyzes ubiquitination of target proteins together with ubiquitin-conjugating enzyme E2 UBE2L3 (By similarity). Acts as an atypical E3 ubiquitin-protein ligase by working together with cullin-5-RING ubiquitin ligase complex (ECS complex, also named CRL5 complex) and initiating ubiquitination of ECS substrates: associates with ECS complex and specifically mediates addition of the first ubiquitin on ECS targets (By similarity). The initial ubiquitin is then elongated (By similarity). E3 ubiquitin-protein ligase activity is activated upon binding to neddylated form of the ECS complex. Mediates 'Lys-6', 'Lys-48'- and 'Lys-63'-linked polyubiquitination. May play a role in myelopoiesis (By similarity). [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. Autoinhibited by the ariadne domain, which masks the second RING-type zinc finger that contains the active site and inhibits the E3 activity (By similarity). Inhibition is relieved upon binding to neddylated cullin-RING ubiquitin ligase complexes, which activate the E3 ligase activity of ARIH1 (By similarity). Protein modification; protein ubiquitination. Interacts (via RING-type zinc finger 1) with UBE2L3. Interacts (via RING-type zinc finger 2) with UBE2N. Interacts with neddylated CUL5. Interacts (via RING-type 2) with GFI1B. Interacts with GFI1; prevents its ubiquitination and proteasomal degradation. Interacts with DCUN1D1 (via UBA-like domain); promotes DCUN1D1 ubiquitination (By similarity). 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. The Ariadne domain inhibits activity by masking the second RING-type zinc finger that contains the active site. Ubiquitinated. Ubiquitination promotes proteasomal degradation. Belongs to the RBR family. Ariadne subfamily.