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 (PubMed:10454532). Probably forms a large corepressor complex that contains ncor1, sin3a, hdac1-A and/or hdac1-B, hdac2, rbbp4-A and/or rbbp4-B and possibly rbbp7 (PubMed:11254656). Belongs to the WD repeat RBAP46/RBAP48/MSI1 family.