E3 ubiquitin-protein ligase which mediates 'Lys-48'-linked ubiquitination of STAT2 and induces its proteosomal degradation thereby negatively regulating type-I-interferon signaling. 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. Interacts with STAT2; the interaction results in STAT2 'Lys-48'-linked ubiquitination leading to its proteasomal degradation. The RING-type zinc finger domain is responsible for E3 ubiquitin ligase activity.