Nucleoplasmin: A Versatile Histone Chaperone

Abstract

Cells have evolved an ingenious way to tightly pack the genetic information in a nucleoprotein complex called chromatin. The functional unit of chromatin is the nucleosome, which is made of DNA wrapped around histones. Dynamic modulation of nucleosome structure by regulating the association/dissociation of histones to/from DNA is essential for DNA replication, repair and transcription. In vivo , a group of histone chaperones facilitate and regulate nucleosome assembly. Recent structural, biophysical and biochemical studies have begun to shed light on the molecular mechanisms whereby histone chaperones promote chromatin assembly, disassembly and histone exchange. This review focuses on the structure and function of Nucleoplasmin (NP), a key component of the amphibian chromatin remodelling machinery during fertilisation and early embryonic development. Key Concepts Histone chaperones are key components of the machinery that regulates chromatin dynamics. The function of histone chaperones is based on their interaction with histone surfaces involved in binding to DNA and other histones. Histone chaperones can be classified into two main groups, specific and generic chaperones, according to their ability to bind only a particular histone or all kind of linker and core histones with similar affinity, respectively. Nucleoplasmin is a generic histone chaperone able to interact with both linker and core histones. Nucleoplasmin uses the same protein region, the intrinsically disordered, acidic distal face to interact with all histones, favouring competition for NP binding and thus histone exchange. The oligomeric structure of NP builds a large histone‐binding region that allows the chaperone to bind different association states of histones, including the octamer.