CHARACTERIZATION OF NUCLEOSOME CORE PARTICLES CONTAINING HISTONE PROTEINS MADE IN BACTERIA

The four core histone proteins, H2A, H2B, H3, and H4 of Xenopus laevis have been individually expressed in milligram quantities in Escherich ia coli. The full-length proteins and the ''trypsin-resistant'' globul ar domains were purified under denaturing conditions and folded into h istone octamers. Both intact and truncated recombinant octamers, as we ll 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 compar ed 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 Angstrom resolution. (C) 1997 Academic Press Limited.