High-resolution structure of the native histone octamer

Abstract

Crystals of native histone octamers (H2A-H2B)-(H4-H3)-(H3′-H4′) -(H2B′-H2A′) from chick erythrocytes in 2 M KCl, 1.35 M potassium phosphate pH 6.9 diffract X-rays to 1.90 Å resolution, yielding a structure with an Rwork value of 18.7% and an Rfree of 22.2%. The crystal space group is P65, the asymmetric unit of which contains one complete octamer. This high-resolution model of the histone-core octamer allows further insight into intermolecular interactions, including water molecules, that dock the histone dimers to the tetramer in the nucleosome-core particle and have relevance to nucleosome remodelling. The three key areas analysed are the H2A′-H3-H4 molecular cluster (also H2A-H3′- H4′), the H4-H2B′ interaction (also H4′-H2B) and the H2A′-H4 β-sheet interaction (also H2A-H4′). The latter of these three regions is important to nucleosome remodelling by RNA polymerase II, as it is shown to be a likely core-histone binding site, and its disruption creates an instability in the nucleosome-core particle. A majority of the water molecules in the high-resolution octamer have positions that correlate to similar positions in the high-resolution nucleosome-core particle structure, suggesting that the high-resolution octamer model can be used for comparative studies with the high-resolution nucleosome-core particle. © 2005 International Union of Crystallography. All rights reserved.