May modulate chromatin structure by regulation of nucleosome assembly/disassembly (By similarity). May function in nucleotide excision repair (NER). Involved in somatic homologous recombination. Could be involved in response to abscisic acid (ABA) and to salt stress. Can form homomeric and heteromeric protein complexes with NAP1;1, NAP1;2 and NAP1;4. Binds histone H2A and associates with chromatin in vivo. Predominantly located in cytoplasm. Ubiquitous. The acidic domain is probably involved in the interaction with histones. No visible phenotype. Exhibits hyposensitive response to abscisic acid (ABA) with defects in stomata closure, and a decreased tolerance to salt stress. Triple mutant nap1;1-nap1;2-nap1;3 has no obvious visible phenotype but exhibits hypersensitivity to DNA damage after UV-radiation, affected transcription of NER related genes (PubMed:19228338), slight hypersensitive response to abscisic acid (ABA) in seedling growth (PubMed:19825649) and impaired somatic homologous recombination (PubMed:22534127). Belongs to the nucleosome assembly protein (NAP) family.