Histone chaperone (By similarity). Plays a role in the epigenetic regulation of gene expression during cellular differentiation, by regulating the acetylation status of histone H3 and therefore chromatin accessibility (PubMed:35032339). Plays a role in the differentiation of neuronal cells (By similarity). Increased activity during aging may suppress osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and promote their senescence; recruits SIRT1 to deacetylate histone H3 'Lys-14' at the promoter of osteogenic genes (PubMed:35032339). {ECO:0000250|UniProtKB:P51860, ECO:0000250|UniProtKB:P55209, ECO:0000269|PubMed:35032339}. This is the function of NAP1L2 (nucleosome assembly protein 1 like 2, Ensembl gene identifier ENSG00000186462).