Rigid Base Pair Monte Carlo Simulations of One-Start and Two-Start Chromatin Fiber Unfolding by Force

The organization of chromatin in 30 nm fibers remains a topic of debate. Here we quantify the mechanical properties of the linker DNA and evaluate the impact of these properties on chromatin fiber folding. We extended a rigid base-pair DNA model to include (un-)wrapping of nucleosomal DNA and (un-)stacking of nucleosomes in one-start and two-start chromatin fibers. Monte Carlo simulations that mimic single-molecule force spectroscopy experiments of folded nucleosomal arrays reveal different stages of unfolding as a function of force and are largely consistent with a two-start folding for 167 and one-start folding for 197 nucleosome repeat length fibers.

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