Temporal Changes in Nucleosome Populations during Sea Urchin Early Development
The finding that the major H2A histone isolated in nucleosomes of a particular developmental stage corresponds to the major H2A subtype synthesized at and prior to that stage [Shaw, B. R., Cognetti, G., Sholes, W. M., & Richards, R. G. (1981) Biochemistry 20, 4971-4978] suggests that the nucleosome population of Strongylocentrotus purpuratus sea urchin embryos becomes increasingly heterogeneous through development. Nuclei from morula, blastula, and prism stages were digested with micrococcal nuclease and the nucleosomes fractionated by their solubility at different ionic strengths (≤0.1 M NaCl). Comparison of the nucleoproteins in the resulting fractions by polyacrylamide gel electrophoresis revealed trends of decreasing solubility and increasing nucleo-protem heterogeneity through development, which paralleled programmed developmental switches in histones. Whereas morula- and blastula-stage chromatins digested to two distinct and relatively stable monomer nucleosome species, prism-stage chromatin exhibited broad heterogeneity in the monomrr nucleosome region. Two-dimensional analysis of proteins from blastula-stage nucleosomes indicated an asymmetric distribution of histone HI and minor amounts of non-histone proteins associated with dimer nucleosome subsets, which were also characterized by differences in their relative mobilities and proportions of H2Aα and H2Bα histones. These results suggested that variations in core histone subtypes may promote nucleosome conformational heterogeneity. © 1984, American Chemical Society. All rights reserved.
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