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 (PubMed:21147464, PubMed:23950712, PubMed:28469175, PubMed:31006531). 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 (PubMed:21147464, PubMed:28469175, PubMed:31006531). 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 (PubMed:31006531). This second mechanism that synergizes with the ubiquitin-dependent one would thereby allow an RNA length-dependent regulation of the RIG-I signaling pathway (PubMed:31006531). Associated with the E2 ligase UBE2N, also constitutively synthesizes unanchored 'Lys-63'-linked polyubiquitin chains that may also activate the RIG-I signaling pathway (By similarity). It is not involved in the innate immune response against DNA viruses (PubMed:21147464). 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. Ubiquitously expressed. 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. Mice lacking Rnf135 develop and breed normally (PubMed:21147464). They are susceptible to RNA viruses infection (PubMed:21147464).