Supercoiling constraints

These results raise the prospect of dynamics of nucleosomes in linker histone-free chromatin, that is, of a thermal fluctuation of nucleosomes between closed negative , open , and closed positive states identified in the minicircle system. If this equilibrium exists, an extra supercoiling constraint applied to the fiber should displace it in one direction or the other depending on the sign of that constraint, and this displacement should be reversible upon its removal. 

A puzzling observation in the above mentioned investigation of the effect of positive supercoiling on nucleosome structure [51] was that the number of nucleosomes 

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