RING-finger E3 ubiquitin ligase that degrades host SP100, one of the major components of ND10 nuclear bodies, thereby disrupting the organization of these bodies. Also plays a role in the inhibition of host NF-kappa-B pathway by blocking the SCF(BTRC)-mediated addition of ubiquitin chains to host IkappaBalpha/NFKBIA, thereby interfering with its degradation. 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. Interacts with host BTRC; this interaction seems to inactivate SCF-mediated protein degradation in general.