Protein dissociation from DNA in model systems and chromatin

Salt induced dissociation of protamine, poly(L-lysine) and poly(L-arginine) from DNA was measured by relative light scattering at θ = 90° and/or centrifugation. Dissociation of histones from DNA was studied using relative light scattering and intrinsic tyrosine fluorescence. Protamine was dissociated from DNA at 0.15 M MgCl<inf>2</inf> (ionic strength μ = 0.45) or 0.53 M NaCl (μ = 0.53) based on light scattering data and at approximately 0.2 M MgCl<inf>2</inf> (μ = 0.6) or 0.6 M NaCl based on centrifugation data. NaCl induced dissociation of poly(Lys) or poly(Arg) from natural DNAs measured by light scattering did not depend on the guanine plus cytosine content. To dissociate poly (Arg) from DNA higher ionic strength using NaCl, MgCl<inf>2</inf> or CaCl<inf>2</inf> similar ionic strength using NaClO<inf>4</inf> and lower ionic strength using Na<inf>2</inf>SO<inf>4</inf> was needed then to dissociate poly(Lys). Both the decrease in light scattering and the enhancement of tyrosine fluorescence of chromatin occurred between 0.5 and 1.5 M NaCl when histones were dissociated.