Component of the histone H2B ubiquitin ligase complex (HULC) which plays a role in transcription regulation by catalyzing the 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. Component of the histone H2B ubiquitin ligase complex (HULC) composed of at least brl1, brl2, rhp6 and shf1.