E3 ubiquitin-protein ligase that mediates monoubiquitination of 'Lys-117' of histone H2B (By similarity). H2B 'Lys-117' ubiquitination gives a specific tag for epigenetic transcriptional activation and is also prerequisite for histone H3 'Lys-4' and 'Lys-79' methylation (By similarity). Involved in regulating stem cell proliferative fate (By similarity). 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 ubc-1 (By similarity). Interacts with mrg-1 (By similarity). Belongs to the BRE1 family.