Abstract
Polystyrene sulfonate (PSS), has been shown in the mealy bug to decondense chromatin and to activate RNA synthesis [1]. Previous work [2] suggests that this decondensation and activation results from interaction of PSS with histone. This paper examines the mechanism of decondensation in hen erythrocyte nuclei prepared by saponin lysis and treated with increasing doses of PSS. Histones were extracted with 0.5 N H 2SO 4 and analysed by polyacrylamide gel electrophoresis. The decreased amount of histone recoverable from PSS treated nuclei indicates that PSS binds to the histone of chromatin in the ratio of 1.0:1.7 on a dry weight basis. The F2 c serine-rich fraction is removed first. The remaining fractions are bound to PSS in the sequence F3, F2 a1, F2 b, F1. Since the F3 histone has been shown to be the most tightly bound to the DNA, it appears that the unique order of extraction with PSS may result from steric interactions rather than from relative binding strengths of DNA and histones. Electron microscopy shows that a loosening of the highly condensed chromatin structure occurs at the concentration of PSS required for binding of the F2 c fraction. Electron microscopic cytochemistry with ammoniacal silver confirms that histones are removed from the chromatin with PSS.
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