May modulate chromatin structure by regulation of nucleosome assembly/disassembly. Can form homomeric and heteromeric protein complexes with NAP1;1, NAP1;2 and NAP1;3. Binds histone H2A. Shuttles between cytoplasm and nucleus. Expressed in the root segment covering the apical end of the differentiation zone, the elongation zone of the root and the mature pollen within the anthers of open flowers. The acidic domain is probably involved in the interaction with histones. Belongs to the nucleosome assembly protein (NAP) family.