E3 ubiquitin-protein ligase, which accepts ubiquitin from specific E2 ubiquitin-conjugating enzymes, such as UBE2L3/UBCM4, and then transfers it to substrates (PubMed:12629548, PubMed:17449468, PubMed:18711448). Functions as an E3 ligase for oxidized IREB2 and both heme and oxygen are necessary for IREB2 ubiquitination (PubMed:12629548). Promotes ubiquitination of TAB2 and IRF3 and their degradation by the proteasome (PubMed:17449468, PubMed:18711448). Component of the LUBAC complex which conjugates linear ('Met-1'-linked) polyubiquitin chains to substrates and plays a key role in NF-kappa-B activation and regulation of inflammation (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181, PubMed:19136968). LUBAC conjugates linear polyubiquitin to IKBKG and RIPK1 and is involved in activation of the canonical NF-kappa-B and the JNK signaling pathways (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181, PubMed:19136968). Linear ubiquitination mediated by the LUBAC complex interferes with TNF-induced cell death and thereby prevents inflammation (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181). LUBAC is recruited to the TNF-R1 signaling complex (TNF-RSC) following polyubiquitination of TNF-RSC components by BIRC2 and/or BIRC3 and to conjugate linear polyubiquitin to IKBKG and possibly other components contributing to the stability of the complex (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181, PubMed:19136968). The LUBAC complex is also involved in innate immunity by conjugating linear polyubiquitin chains at the surface of bacteria invading the cytosol to form the ubiquitin coat surrounding bacteria (PubMed:28481331). LUBAC is not able to initiate formation of the bacterial ubiquitin coat, and can only promote formation of linear polyubiquitins on pre-existing ubiquitin (PubMed:28481331). The bacterial ubiquitin coat acts as an 'eat-me' signal for xenophagy and promotes NF-kappa-B activation (PubMed:28481331). Together with OTULIN, the LUBAC complex regulates the canonical Wnt signaling during angiogenesis (PubMed:23708998). Binds polyubiquitin of different linkage types (PubMed:20005846, PubMed:21455181). [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. Protein modification; protein ubiquitination. Component of the LUBAC complex (linear ubiquitin chain assembly complex) which consists of SHARPIN, RBCK1 and RNF31 (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181, PubMed:28481331, PubMed:22430200). LUBAC has a MW of approximately 600 kDa suggesting a heteromultimeric assembly of its subunits (PubMed:17006537, PubMed:21455173, PubMed:21455180, PubMed:21455181). Interacts with beta-I-type (PRKCB1) and zeta-type protein kinase C (PRKCZ) (By similarity). Interacts with UBE2L3 (By similarity). Interacts with PRKCH (PubMed:9195957). Associates with the TNF-R1 signaling complex (TNF-RSC) in a stimulation-dependent manner (PubMed:20005846). Interacts with EYA1, TAB2, TAB3, MAP3K7 TRAF6 and RIPK1 (PubMed:17449468). Interacts with IRF3 (PubMed:18711448). Interacts with IREB2 only in iron-rich conditions. Interacts with IREB2 only in iron-rich conditions. (Microbial infection) Interacts with S.flexneri E3 ubiquitin-protein ligases IpaH1.4 and IpaH2.5, leading to its ubiquitination. (Microbial infection) Interacts with hepatitis B virus/HBV protein HBx; this interaction is required to activate transcription of the viral genome. Experimental confirmation may be lacking for some isoforms. By viral transfection. The RanBP2-type zinc finger, also called Npl4 zinc finger (NZF), mediates binding to 'Met-1'-linked polyubiquitins. The UBL domain mediates association with RNF31 via interaction with its UBA domain. Auto-ubiquitinated. Auto-ubiquitination leads to degradation by the proteasome (By similarity). Phosphorylated. In vitro, phosphorylation inhibits auto-ubiquitination activity (By similarity). The disease is caused by variants affecting the gene represented in this entry. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the RBR family. Truncated N-terminus.