Histone chaperone that facilitates histone deposition and histone exchange and removal during nucleosome assembly and disassembly (PubMed:12842904, PubMed:17054786). Cooperates with chromatin assembly factor 1 (CAF-1) to promote replication-dependent chromatin assembly (By similarity). Also involved in the nuclear import of the histone H3-H4 dimer together with importin-4 (IPO4): specifically recognizes and binds newly synthesized histones with the monomethylation of H3 'Lys-9' (H3K9me1) and diacetylation at 'Lys-5' and 'Lys-12' of H4 (H4K5ac and H4K12ac) marks in the cytosol (By similarity). Does not participate in replication-independent nucleosome deposition which is mediated by ASF1A and HIRA (By similarity). Required for gonad development (PubMed:26850882). Interacts with histone H3 (including both histone H3.1 and H3.3) and histone H4 (By similarity). Interacts with the CHAF1A, CHAF1B and RBBP4 subunits of the CAF-1 complex (By similarity). Interacts with HAT1, NASP and TAF1 (By similarity). Interacts with CDAN1. Found in a cytosolic complex with CDAN1, ASF1A, IPO4 and histones H3.1 and H4 (By similarity). Interacts with CREBBP (By similarity). Highly expressed in germ cells (PubMed:26850882). Restricted to premeiotic to meiotic stages during spermatogenesis (PubMed:12842904). Expressed in early embryos and germ cells. Phosphorylated by TLK2 (By similarity). Phosphorylated by TLK1 (PubMed:17054786). Mice are viable but display subfertility caused by altered gamete formation (PubMed:26850882). The timing of meiotic entry and the subsequent gonad development is more severely impaired in female than in male mice (PubMed:26850882). Increased perinatal lethality is also increased in the offspring of knockout females (PubMed:26850882). Belongs to the ASF1 family.