Acts as a chaperone for histones, such as histone H2A-H2B, and thus regulates the assembly of nucleosome cores (PubMed:11684019, PubMed:19055325). Involved in chromatin remodeling, especially during fertilization and early embryonic development (By similarity). May be involved in sperm chromatin decondensation during fertilization (PubMed:17510054). Thermostable. Homopentamer, when bound to H2A-H2B dimers only. Homodecamer of two stacked pentamers, when bound to H2A-H2B dimers and H3-H4 tetramers simultaneously. Interacts with the heterotetramer formed by wdr77 and prmt5. Activated by phosphorylation of multiple serine/threonine residues, along both core and tail domains. The level of phosphorylation gradually increases during egg maturation, reaching an average of 7-10 phosphates per monomer, so that at the time of fertilization the activity of the protein is maximum. Methylated by prmt5, yielding both monomethylated and symmetrically dimethylated Arg-192. Belongs to the nucleoplasmin family.