Component of the chromatin assembly factor complex (CAF-1) involved in chromatin assembly following DNA replication and DNA repair. Required for several aspects of development, including apical meristem maintenance by regulating the durations of the S- and G2-phases of the cell cycle through its chromatin assembly activity (By similarity). Component of the chromatin assembly factor 1 (CAF-1) complex, composed of FSM (FAS1), FAS2 and MSI1. Belongs to the WD repeat HIR1 family.