May be required for maintaining multiple types of adult stem cells. May function as a transcriptional repressor by continually deubiquiting histone H2B at the promoters of genes critical for cellular differentiation, thereby preventing histone H3 'Lys-4' trimethylation (H3K4). Belongs to the peptidase C19 family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.