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Zusammenfassung:
We propose that the degree of swelling of the 30 nm 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.
