May modulate chromatin structure by regulation of nucleosome assembly/disassembly (By similarity). Contributes to the regulation of cell proliferation and cell expansion. May function in nucleotide excision repair (NER). Involved in somatic homologous recombination. Can form homomeric and heteromeric protein complexes with NAP1;2, NAP1;3 and NAP1;4. Binds histone H2A. Interacts with PP438/PNM1. Predominantly located in cytoplasm. Shuttles between cytoplasm and nucleus depending on stage of the cell cycle. Farnelysation favors the location to the nucleus early in leaf development. A number of isoforms are produced. According to EST sequences. Ubiquitous. By brassinosteroids. The acidic domain is probably involved in the interaction with histones. Prenylation of the protein is required for its function during the cell proliferation phase of leaf development. No visible phenotype (PubMed:19228338). Enlarged plants early in the development but reduced plants in size in a later stage (PubMed:17041028). 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. Extended N-terminus.