Histone‐induced conformational changes in DNA as probed by quasi‐elastic light scattering

Quasi‐elastic light scattering as measured by intensity fluctuation (self‐beat) spectroscopy in the time domain can be profitably used to follow both the translational diffusion D and the dominant internal flexing mode τ int of DNA and its complexes with various histones in aqueous salt solutions. Without histones, DNA is found to have D = 1.6 × 10 −8 cm 2 /sec and τ int ≅ 5 × 10 −4 sec in 0.8 M NaCl, 2 M urea at 20°C. Total histone as well as fraction F2A induce supercoiling ( D = 2.6 × 10 −8 cm 2 /sec, τ int ≅ 2.8 × 10 −4 sec) whereas fraction F1 induces uncoiling ( D = 1.0 × 10 −8 cm 2 /sec, τ int ≅ 9.4 × 10 −4 sec). Upon increasing the salt concentration to 1.5 M the DNA–histone complex dissociates ( D = 1.8 × 10 −8 cm 2 /sec). Upon decreasing the salt concentration to far below 0.8 M , the DNA–histone complex eventually precipitates as a chromatin gel.