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 several complexes which regulate chromatin metabolism (By similarity). Probably binds directly to helix 1 of the histone fold of histone H4, a region that is not accessible when H4 is in chromatin. Belongs to the WD repeat RBAP46/RBAP48/MSI1 family.