RING-finger E3 ubiquitin-protein ligase that plays an major role in maintaining COP1 homeostasis in darkness. Negatively regulates COP1 protein accumulation by targeting COP1 for ubiquitination and subsequent proteasomal degradation in dark-grown seedlings. Negatively regulates the accumulation of SPA1 protein in the dark. 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. Is recruited to nuclear speckles by COP1 in the dark. Belongs to the NOSIP family.