Characterization of nucleosome core particles containing histone proteins made in bacteria 1 1Edited by A. Klug

The four core histone proteins, H2A, H2B, H3, and H4 of Xenopus laevis have been individually expressed in milligram quantities in Escherichia coli. The full-length proteins and the “trypsin-resistant” globular domains were purified under denaturing conditions and folded into histone octamers. Both intact and truncated recombinant octamers, as well as chicken erythrocyte octamer, were assembled into nucleosome core particles using a 146 bp defined-sequence DNA fragment from a 5 S RNA gene. The three types of core particles were characterized and compared by gel electrophoresis, DNase I cleavage, and tyrosine fluorescence emission during stepwise dissociation with increasing ionic strength. Nucleosome core particles containing native and mutant histones made in bacteria have facilitated its X-ray structure determination at 2.8 Å resolution.