Preparation of nucleosome core particle from recombinant histones

This chapter describes the preparation method of nucleosome core particles (NCPs) from recombinant histones. The ability to make defined NCPs, or arrays of nucleosomes, from histone proteins expressed in bacteria has several advantages over previously used methods using histones isolated from natural sources. The chapter discusses protocols for the overexpression and purification of histones H2A, H2B, H3, and H4, both as full-length proteins and as corresponding trypsin-resistant globular domains. The chapter presents a method for the refolding and purification of a histone octamer from denatured recombinant histone proteins together with a protocol for the assembly and purification of a nucleosome core particle using 146 base pairs of DNA. The purity and homogeneity of the final core-particle preparation are assessed by a high-resolution gel shift assay. The chapter presents a flow chart that describes the procedures involved in the preparation of synthetic nucleosomes.