BAP1 and neoplasm: BAP1 also binds the epigenetic scaffolding proteins additional sex combs-like-1/2/3 (ASXL1/2/3) to form the polycomb repressive deubiquitinase (PR-DUB) complex that exerts an essential tumour suppressor activity by regulating ubiquitination levels of histone H2A (H2AK119Ub) (Scheuermann et al., 2010).