Nucleosome reconstitution: effect of DNA length on nucleosome structure

Abstract

Core histones [from chicken erythrocyte nuclei] (H2A, H2B, H3 and H4) are reconstituted by salt gradient dialysis with NDA molecules ranging in length from 177 bp [base-pairs] down to 50 bp. While reconstituted particles containing 125 bp are very similar to native particles, those particles containing a single piece of shorter DNA tend to aggregate. The aggregation depends on ionic strength and DNA length. The DNA placement on the histone core is not random as determined by pancreatic DNase I digestions of particles containing 32P 5''-end-labeled DNA. All DNA molecules, up to 161 bp in length, reassociate with core histones in such a way as to produce defined patterns of DNase I cutting with respect to the 5'' ends. Particles were made that contained 2 pieces of 65-bp DNA. These particles are very similar to native particles under most conditions but tended to dissociate at very low ionic strength. This dissociation may result in the production of 2 half-nucleosomes (hemisomes).