Histone chaperone which acts as a cofactor stimulating histone H3 acetylation by RTT109 (PubMed:21256037, PubMed:17320445, PubMed:31387991, PubMed:29300933, PubMed:19172748). Preferentially stimulates histone H3 'Lys-9' acetylation by RTT109 (PubMed:21256037, PubMed:31387991, PubMed:29300933). May also stimulate histone H3 'Lys-56' acetylation by RTT109 (PubMed:17320445). Assembles nucleosomes (in vitro) (PubMed:19172748). Homodimer (PubMed:31387991, PubMed:21256037, PubMed:21454705, PubMed:19172748). Homotetramer (PubMed:27036862). Forms a complex with RTT109; consisting of a VPS75 dimer contacted by two RTT109 subunits (PubMed:21256037, PubMed:20560668, PubMed:17320445, PubMed:31387991, PubMed:18719104, PubMed:21454705). Interacts with RTT109; the interaction is direct (PubMed:20560668, PubMed:17272723, PubMed:17320445, PubMed:31387991, PubMed:18719104, PubMed:21256037). Interacts with ASF1 (PubMed:31387991). Interacts with histone H3/H4 heterodimers and heterotetramers via histone H3 (PubMed:31387991, PubMed:21454705, PubMed:27036862). The C-terminal part interacts with the N-terminal part of histone H3 and promotes acetylation of histone H3 'Lys-9'. Decreases acetylation of histone H3 'Lys-9' and 'Lys-23' (PubMed:19172748). Simultaneous disruption of GCN5 abolishes acetylation of histone H3 'Lys-9' and 'Lys-27' (PubMed:21256037). Abnormal protein sorting to vacuole (PubMed:12134085). Present with 3120 molecules/cell in log phase SD medium. Belongs to the nucleosome assembly protein (NAP) family.