Circular dichroism as a probe of DNA structure inside reconstituted nucleohistones

Reconstituted nucleohistones were obtained by mixing in given conditions acid extracted histones and eukaryotic DNA. The histone/DNA ratio (w/w) was in the range 0.35 - 0.95. With the four histones (H2A2B) we have been able to obtain subunits (nucleosomes or upsilon-bodies). The variation of cirsular dichroism signal with temperature at 280 nm was measured to follow structural changes of the DNA inside the complex. The true change of ellipticity (see article) of histone-bound DNA regions, is similar for reconstituted nucleohistone and H1-depleted chromatin, and is therefore a physical probe of the presence of nucleosomes.