Histone chaperone that facilitates histone deposition and histone exchange and removal during nucleosome assembly and disassembly (PubMed:10759893, PubMed:11897662, PubMed:12842904, PubMed:14718166, PubMed:15664198, PubMed:16151251, PubMed:21454524). Cooperates with chromatin assembly factor 1 (CAF-1) to promote replication-dependent chromatin assembly and with HIRA to promote replication-independent chromatin assembly (PubMed:11897662, PubMed:14718166, PubMed:15664198). Promotes homologous recombination-mediated repair of double-strand breaks (DSBs) at stalled or collapsed replication forks: acts by mediating histone replacement at DSBs, leading to recruitment of the MMS22L-TONSL complex and subsequent loading of RAD51 (PubMed:29478807). 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' and acetylation at 'Lys-14' (H3K9me1K14ac) marks, and diacetylation at 'Lys-5' and 'Lys-12' of H4 (H4K5K12ac) marks in the cytosol (PubMed:21454524, PubMed:29408485). Required for the formation of senescence-associated heterochromatin foci (SAHF) and efficient senescence-associated cell cycle exit (PubMed:15621527). Interacts with histone H3 (including both histone H3.1 and H3.3) and histone H4 (PubMed:10759893, PubMed:12842904, PubMed:14718166, PubMed:15664198, PubMed:33857403, PubMed:15840725). Interacts with the CHAF1A, CHAF1B and RBBP4 subunits of the CAF-1 complex (PubMed:11897662, PubMed:16980972). Interacts with CABIN1, HAT1, HIRA, NASP, TAF1 and UBN1 (PubMed:12093919, PubMed:14680630, PubMed:14718166, PubMed:15621527, PubMed:16980972, PubMed:19029251). Interacts with CDAN1 (PubMed:22407294). Found in a cytosolic complex with IPO4 and histones H3 and H4 (PubMed:21454524, PubMed:22407294). Interacts with CREBBP (PubMed:24616510). Ubiquitously expressed. Phosphorylated by TLK1 and TLK2 (PubMed:11470414, PubMed:20016786). Highly phosphorylated in S-phase and at lower levels in M-phase (PubMed:11470414). TLK2-mediated phosphorylation at Ser-192 prevents proteasome-dependent degradation (PubMed:20016786). Phosphorylation at Ser-192 by PRKDC in response to DNA damage promotes the histone chaperone activity and ability to replace histones at double-strand breaks (DSBs) at stalled or collapsed replication forks, leading to RAD51 recruitment (PubMed:29478807). Belongs to the ASF1 family.