How short-ranged electrostatics controls the chromatin structure on much larger scales

We propose that the degree of sweeling of the 30nm chromatin fiber (a "measure" of its transcriptional activity) is mainly determined by the short-ranged electrostatical interaction between different sections of the "folded" DNA chain. These sections constitute only a small fraction of the chain and they are located close to the entry-exit points of the DNA chain at the nucleosome core particles. We present a model that allows to estimate the degree of swelling of chromatin fibers as a function of salt concentration, charge density of the strands etc. Different mechanisms by which the state of chromatin can be controlled in vitro and in vivo are discussed.