The function of ARIH2 (ariadne RBR E3 ubiquitin protein ligase 2, Ensembl gene identifier ENSG00000177479) is as follows. E3 ubiquitin-protein ligase, which catalyzes ubiquitination of target proteins together with ubiquitin-conjugating enzyme E2 UBE2L3 (PubMed:16118314, PubMed:17646546, PubMed:19340006, PubMed:24076655, PubMed:33268465, PubMed:34518685, PubMed:38418882). 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 (PubMed:33268465, PubMed:34518685, PubMed:38418882). The initial ubiquitin is then elongated (PubMed:33268465). E3 ubiquitin- protein ligase activity is activated upon binding to neddylated form of the cullin-5 (CUL5) component of the ECS complex (PubMed:24076655). Together with the ECS(ASB9) complex, catalyzes ubiquitination of CKB (PubMed:33268465). Promotes ubiquitination of DCUN1D1 (PubMed:30587576). Mediates 'Lys-6', 'Lys-48'- and 'Lys-63'-linked polyubiquitination (PubMed:16118314, PubMed:17646546, PubMed:19340006). May play a role in myelopoiesis (PubMed:19340006). {ECO:0000269|PubMed:16118314, ECO:0000269|PubMed:17646546, ECO:0000269|PubMed:19340006, ECO:0000269|PubMed:24076655, ECO:0000269|PubMed:30587576, ECO:0000269|PubMed:33268465, ECO:0000269|PubMed:34518685, ECO:0000269|PubMed:38418882}. (Microbial infection) Following infection by HIV-1 virus, acts together with a cullin-5-RING E3 ubiquitin-protein ligase complex (ECS complex) hijacked by the HIV-1 Vif protein, to catalyze ubiquitination and degradation of APOBEC3F and APOBEC3G. .