Histone chaperone that plays a role in the nuclear import of H2A-H2B and nucleosome assembly. Participates also in several important DNA repair mechanisms: greatly enhances ERCC6-mediated chromatin remodeling which is essential for transcription-coupled nucleotide excision DNA repair. Stimulates also homologous recombination (HR) by RAD51 and RAD54 which is essential in mitotic DNA double strand break (DSB) repair (By similarity). Plays a key role in the regulation of embryonic neurogenesis (PubMed:29490266). Promotes the proliferation of neural progenitors and inhibits neuronal differentiation during cortical development (PubMed:29490266). Regulates neurogenesis via the modulation of RASSF10; regulates RASSF10 expression by promoting SETD1A-mediated H3K4 methylation at the RASSF10 promoter (PubMed:29490266). Homodimer. The dimer binds strongly and sequentially to single and double H2A-H2B heterodimers. Interacts with ERCC6; this interaction increases ERCC6 processivity. Interacts with RAD54 (By similarity). Interacts with SETD1A (PubMed:29490266). Highly expressed in the brain (at protein level) (PubMed:29490266). High expression in cerebral cortex, not in cerebellar cortex. During brain development, expression decreases from 12 dpc to P0. Expressed predominantly but not restricted in the ventricular zone (VZ)/subventricular zone (SVZ), and peak expression is observed at 12.5 dpc, in which the cerebral cortex consists primarily of neural progenitor cells (NPCs). At 15.5 dpc, the expression decreases in the cerebral cortical plate. At 18.5 dpc, when the embryonic neurogenesis period nears its end, the expression throughout the cerebral cortex is lower than that at 12.5 dpc (at protein level). The acidic domains are probably involved in the interaction with histones. Polyglycylated by TTLL10 on glutamate residues, resulting in polyglycine chains on the gamma-carboxyl group. Both polyglutamylation and polyglycylation modifications can coexist on the same protein on adjacent residues, and lowering polyglycylation levels increases polyglutamylation, and reciprocally. Polyglutamylated by TTLL4 on glutamate residues, resulting in polyglutamate chains on the gamma-carboxyl group. Both polyglutamylation and polyglycylation modifications can coexist on the same protein on adjacent residues, and lowering polyglycylation levels increases polyglutamylation, and reciprocally. Mice show abnormal embryonic neurogenesis. Belongs to the nucleosome assembly protein (NAP) family.