1. 1. DNA crosslinked by trioxalen and u.v. light irradiation has been thermally denatured at low Nad concentrations-1 mM NaCl to 30 mM NaCl. The slope of tm vs pNa+ diners from that for free DNA. 2. 2. A similar dependence of tm is found for the first transition in the melting profile of partially deproteinized chromatin. 3. 3. The change in the slope is discussed in terms of recent polyelectrolite theory. 4. 4. The results are an additional evidence that denaturation of naked DNA regions is the main source of the first transition in the denaturation profile of histone Hl-depleted chromatin.
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