[Study of the process of chromatin condensation using light scattering and stop-flow technics]

We have studied the condensation of calf thymus chromatin induced by NaCl by static light scattering at 90 degrees and showed that the increase of NaCl concentration up to 120-170 mM results in a large increase of scattering intensity of the total chromatin. H1-depleted and trypsinized chromatin preparations do not reveal such a large increase of scattering intensity. The increase of the scattering intensity reflects folding of the chromatin filaments, but not their aggregation. We have used this effect to monitor the kinetics of the chromatin condensation in response to a jump to higher NaCl concentrations by means of a stopped-flow technique. The results show that the condensation is a fast complex process consisting of at least two steps. The first step is only partially resolved by the stopped-flow apparatus. The second step has a time constant in the range of 20-50 ms and does not depend on chromatin concentration.