The condensation of the 10 nm chromatin filament in the 30 nm fiber by monovalent cations, polyamines and bivalent cations was studied with light scattering at 90° and flow linear dichroism methods. It was found that monovalent cation- and polyamine-induced folding was a two-step process: a precondensation, when a rotation of nucleosomes takes place only, and a condensation step without changes in nucleosome orientation. Divalent cations affected the structure of chromatin in one step only - condensation of the chromatin filament being accompanied by nucleosome reorientation.
