E3 ubiquitin-protein ligase which belongs to the histone H2B ubiquitin ligase complex (HULC) which mediates monoubiquitination of histone H2B to form H2BK123ub1. H2BK123ub1 gives a specific tag for epigenetic transcriptional activation and is also a prerequisite for H3K4me and H3K79me formation. 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. Component of the histone H2B ubiquitin ligase complex (HULC) composed of at least brl1, brl2, rhp6 and shf1. Belongs to the BRE1 family.