NaCl-induced chromatin condensation. Application of static light scattering at 90 degrees and stopped flow technique

We have studied the NaCl-induced condensation of calf thymus chromatin by static light scattering of 90 degrees and shown that the increase in NaCl concentration up to 120-170 mM results in a large increase in scattering intensity of the total chromatin. Histones H1-depleted and trypsinized chromatin preparations do not reveal such a large increase in scattering intensity. The increase in the scattering intensity reflects the 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, which does not depend on chromatin concentration.