The crystal structure of nucleoplasmin-core: Implications for histone binding and nucleosome assembly

The efficient assembly of histone complexes and nucleosomes requires the pa rticipation of molecular chaperones. Currently, there is a paucity of data on their mechanism of action. We now present the structure of an N-terminal domain of nucleoplasmin (Np-core) at 2.3 Angstrom resolution. The Np-core monomer is an eight-stranded beta barrel that fits snugly within a stable p entamer. In the crystal, two pentamers; associate to form a decamer. We sho w that both Np and Np-core are competent to assemble large complexes that c ontain the four core histones. Further experiments and modeling suggest tha t these complexes each contain five histone octamers; which dock to a centr al Np decamer. This work has important ramifications for models of histone storage, sperm chromatin decondensation, and nucleosome assembly.