Probable ubiquitin-protein ligase involved in the degradation-related ubiquitination of histones. Contributes to the post-translational regulation of histone protein levels by polyubiquitination of excess histones for subsequent 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. Protein modification; protein ubiquitination. Interacts with the E2 ubiquitin-conjugating enzyme UBC4 and histones H3 and H4. Present with 1960 molecules/cell in log phase SD medium.