Retinoblastoma associated proteins 46 and 48 (RBAP46 and RBAP48; also known as RBBP7 and RBBP4) were first characterized in human cells as proteins that bind to the retinoblastoma (Rb) tumor suppressor protein. Since then, these proteins have been shown to be components of many protein  complexes involved in  chromatin  regulation, including the chromatin  assembly factor 1 (CAF­1) complex and type B histone acetyltransferase complex HAT1, both of which function in chromatin  assembly during DNA  replication. RBAP46 and RBAP48 are also found in the nucleosome remodeling factor complex NURF, the nucleosome remodeling and histone de­acetylation complex NuRD, and the Sin3/HDAC histone de­acetylation complex. More recently, RBAP46 and RBAP48 were identified as components of the polycomb repressor complex PRC2, which also contains EED and Ezh2. RBAP46 and RBAP48 bind to the histone fold region of histone H4 and are believed to target these chromatin remodeling, histone acetylation, and histone de­acetylation complexes to their histone substrates.