Modulation of nucleosome structure by histone subtypes in sea urchin embryos.

Open Access
Publisher Website
Google Scholar
Abstract
Switches of the types of histones synthesized and incorporated into chromatin occur during sea urchin embryogenesis. In an attempt to define the possible effects of these variant histones on chromatin structure, nucleosome core particles were isolated and characterized from S. purpuratus blastula (nearly 100% early histones) and pluteus (75% late histones). Both particles contain 146-base-pair lengths of DNA wrapped around an octamer of H2A, H2B, H3 and H4. Although sharing these similarities with the canonical core particle, the nucleosome structures also differ from those of typical adult tissues. The reversible and the irreversible conformational transitions occurring on heating core particles are destabilized in the embryonic particles vs. typical core particles. The blastula core particle unfolds more easily than pluteus (or other) nucleosomes under the stress of low ionic strength. The rate of DNase I digestion of pluteus core particles is about half that of particles from blastula; certain cutting sites differ in their susceptibility between the 2 embryonic particles and between these two and the canonical core particle. The variant histones synthesized during early embryogenesis have demonstrable effects on chromatin structure, even at this basic level.