The size of the nucleosome

TL;DR

This paper proposes a mathematical model explaining the size of nucleosomes based on DNA packing efficiency and mechanical stability, aligning well with experimental measurements and highlighting DNA's intrinsic properties.

Contribution

It introduces a novel model linking nucleosome size to DNA's molecular interactions and mechanical constraints, providing a physical basis for nucleosome dimensions.

Findings

Model predicts nucleosome size consistent with experimental data

Nucleosome size arises from DNA's intrinsic properties

Zero strain-twist condition is crucial for nucleosome stability

Abstract

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.