Abstract
Winding DNA in a superhelix can be considered a process consisting of two smooth deformations: bending and twisting. The extra twist angle introduced by winding DNA into the nucleosomal superhelix is calculated by means of the Crick formula to be −0.5° per base pair (bp). This is equivalent to a change of −0.15±0.015 bp in the DNA double-helical repeat. Free DNA in solution is known to have a helical repeat of 10.55±0.1 bp. On the other hand, a weighted average of various estimates of the DNA repeat in the nucleosome is 10.38±0.02. The difference happens to be perfectly accounted for by the superhelicity of the nucleosomal DNA. This implies that the latter is essentially nonconstrained.
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Trifonov, E. N. (submitted for publication).
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Ulanovsky, L.E., Trifonov, E.N. Superhelicity of nucleosomal DNA changes its double-helical repeat. Cell Biophysics 5, 281–283 (1983). https://doi.org/10.1007/BF02788626
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DOI: https://doi.org/10.1007/BF02788626