Histone chaperone that facilitates histone deposition and histone exchange and removal during nucleosome assembly and disassembly. Cooperates with chromatin assembly factor 1 (CAF-1) to promote replication-dependent chromatin assembly. May also cooperate with HIRA to promote replication-independent chromatin assembly. Interacts with CHAF1B, HIRA, histone H3 and histone H4. Phosphorylated. Belongs to the ASF1 family.