E2-dependent E3 ubiquitin-protein ligase that functions as a RIG-I/DDX58 coreceptor in the sensing of viral RNAs in cell cytoplasm and the activation of the antiviral innate immune response. Together with the UBE2D3, UBE2N and UB2V1 E2 ligases, catalyzes the 'Lys-63'-linked polyubiquitination of RIG-I/DDX58 oligomerized on viral RNAs, an essential step in the activation of the RIG-I signaling pathway. Through a ubiquitin-independent parallel mechanism, which consists in bridging RIG-I/DDX58 filaments forming on longer viral RNAs, further activates the RIG-I signaling pathway. This second mechanism that synergizes with the ubiquitin-dependent one would thereby allow an RNA length-dependent regulation of the RIG-I signaling pathway. Associated with the E2 ligase UBE2N, also constitutively synthesizes unanchored 'Lys-63'-linked polyubiquitin chains that may also activate the RIG-I signaling pathway. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Homodimer. Interacts (homodimer) with DDX58 (double-stranded RNA-bound oligomeric form); involved in both DDX58 ubiquitination, oligomerization into filaments associated with viral RNAs and the bridging of these filaments. Interacts with UBE2D3 and UBE2N; E2 ubiquitin ligases involved in RNF135-mediated ubiquitination of DDX58 and activation of the RIG-I signaling pathway. Interacts with PCBP2. The B30.2/SPRY domain mediates the interaction with the substrate RIG-I/DDX58. The coiled-coil domains mediate homodimerization and the bridging of viral RNA-associated RIG-I/DDX58 filaments.