Core histone-binding subunit that may target chromatin assembly factors, chromatin remodeling factors and histone deacetylases to their histone substrates in a manner that is regulated by nucleosomal DNA. Component of the DREAM complex (By similarity). Binds directly to histone H4, probably via helix 1 of the histone fold, a region that is not accessible when histone H4 is in chromatin (By similarity). Forms a large corepressor complex that contains ncor1, sin3a and possibly sin3b, histone deacetylases hdac2, hdac1, rbbp4 and possibly rbbp7 (By similarity). Belongs to the WD repeat RBAP46/RBAP48/MSI1 family.