  Understanding chromatin organization and dynamics is important since they
crucially affect DNA functions. In this study, we investigate chromatin
dynamics by statistically analyzing single-nucleosome movement in living human
cells. Bi-modal nature of the mean squared displacement distribution of
nucleosomes allows for a natural categorization of the nucleosomes as fast and
slow. Analyses of the nucleosome-nucleosome correlation functions within these
categories along with the density of vibrational modes show that the
nucleosomes form dynamically correlated fluid regions, i.e., dynamic domains of
fast and slow nucleosomes. Perturbed nucleosome dynamics by global histone
acetylation or cohesin inactivation indicate that nucleosome-nucleosome
interactions along with tethering of chromatin chains organize nucleosomes into
fast and slow dynamic domains. A simple polymer model is introduced, which
shows the consistency of this dynamic domain picture. Statistical analyses of
single-nucleosome movement provide rich information on how chromatin is
dynamically organized in a fluid manner in living cells.
