The structural origin of the size of the 11 nm nucleosomal disc is addressed.
On the nanometer length-scale the organization of DNA as chromatin in the
chromosomes involves a coiling of DNA around the histone core of the
nucleosome. We suggest that the size of the nucleosome core particle is
dictated by the fulfillment of two criteria: One is optimizing the volume
fraction of the DNA double helix; this requirement for close-packing has its
root in optimizing atomic and molecular interactions. The other criterion being
that of having a zero strain-twist coupling; being a zero-twist structure is a
necessity when allowing for transient tensile stresses during the
reorganization of DNA, e.g., during the reposition, or sliding, of a nucleosome
along the DNA double helix. The mathematical model we apply is based on a
tubular description of double helices assuming hard walls. When the base-pairs
of the linker-DNA is included the estimate of the size of an ideal nucleosome
is in close agreement with the experimental numbers. Interestingly, the size of
the nucleosome is shown to be a consequence of intrinsic properties of the DNA
double helix.Comment: 11 pages, 5 figures; v2: minor modification
