The accessibility of DNA is regulated by means of dynamic folding and unfolding of chromatin fibers. Quantification of chromatin unfolding is a key in understanding the higher order structure of...Show moreThe accessibility of DNA is regulated by means of dynamic folding and unfolding of chromatin fibers. Quantification of chromatin unfolding is a key in understanding the higher order structure of chromatin. Single molecule force spectroscopy is an ideal tool to study chromatin dynamics. The extension of reconstituted chromatin fibers under force was measured using Magnetic Tweezers. Here I show a model to fit discrete states in chromatin unfolding, and use this model to quantify the influence of linker histone H1 on chromatin fibers. Stepsize analysis revealed that linker histone H1 induces cooperative unstacking of nucleosomes at forces less than 10 pN. Chromatin fibers in presence of linker histone H1 must be stretched $4.5\pm0.8$ nm for two nucleosomes to unstack. This model can be used to quantify natively folded chromatin fibers.Show less