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. These include the chromatin assembly factor 1 (CAF-1) complex, which is required for chromatin assembly following DNA replication and DNA repair, and the fertilization independent seed (FIS) complex, a polycomb group protein complex which is required to maintain the transcriptionally repressive state of homeotic genes throughout development. Required for several aspects of plant development including normal leaf expansion, correct development of flowers, normal endosperm development, repression of parthenogenetic seed development and repression of floral homeotic genes in leaf tissue. Also required for the recruitment of chromosomal DNA into heterochromatic chromocenters. Also involved in regulation of imprinted genes. Acts together with RBR1 to repress the expression of MET1 during female gametogenesis. This in turn activates expression of the imprinted genes FIS2 and FWA. Binds directly to helix 1 of the histone fold of histone H4, a region that is not accessible when H4 is in chromatin (By similarity). Component of the chromatin assembly factor 1 (CAF-1) complex, composed of FAS1, FAS2 and MSI1. Component of the FIS complex which includes at least MEA, FIE, MIS1 and possibly FIS2. Interacts with EMF1. Component of the plant homeodomain / polycomb repressive complex 2 (PHD-PRC2) large complex during prolonged cold, composed of core PRC2 components (VRN2, EZA1, FIE and MSI1), and three related PHD finger proteins (VIL1, VIL2 and VIN3) that mediates histone H3 trimethylation on 'Lys-27' H3K27me3. Interacts with RBR1. Binds to ALP1 (PubMed:26642436). Ubiquitously expressed. Strongly expressed in floral buds and flowers, the female gametophyte and the sporophytic tissue of the ovules. Also strongly expressed in developing embryos following fertilization. Expressed during female gametophyte development. The DWD box is required for interaction with DDB1A. Belongs to the WD repeat RBAP46/RBAP48/MSI1 family.