Dynamics of Nucleosomes and Chromatin Fibers Revealed by Single-Molecule Measurements.

Abstract

The nucleosome is the fundamental structural unit of chromosome fibers. A DNA wraps around a histone octamer to form a nucleosome, while neighboring nucleosomes interact to form higher-order structures and fit gigabase-long DNAs into a small volume of the nucleus. Nucleosomes interrupt the access of transcription factors to a genomic region, and provide regulatory controls of gene expression. Biochemical and physical cues stimulate wrapping-unwrapping and condensation-decondensation dynamics of nucleosomes and nucleosome arrays. Nucleosome dynamics and chromatin fiber organization are influenced by changes in the ionic background within the nucleus, post-translational modifications of histone proteins, and DNA sequence characteristics, such as histone-binding motifs and nucleosome spacing. Biochemical and biophysical measurements, along with in silico simulations, have been extensively used to study the regulatory effects on chromatin dynamics. In particular, single-molecule measurements have revealed novel mechanistic details of nucleosome and chromatin dynamics. This minireview elucidates recent findings on chromatin dynamics from these approaches.