Single Molecule Mechanical Measurement of Inter-Nucleosome Interaction

Histone proteins assemble on DNAs to form arrays of nucleosomes and control the accessibility of the bound regions to transcription machineries. Thus, understanding how the nucleosome wrapping/positioning and the compaction of nucleosome arrays are controlled is the key to understanding epigenetic gene regulation. Each histone protein has unstructured tail region, which are active and multiplexed targets of various types of epigenetic chemical modifications. We still lack understanding of the mechanical control of DNA conformation by the modification of these histone tails. To measure the mechanical properties and dynamics of chromatin fibers modulated by histone tails, we developed single molecule magnetic tweezers combined with single molecule fluorescence imaging. We engineered the tail regions of histone proteins, either by deleting the tail regions or by chemically modifying specific residues, in order to assess their roles in controlling chromatin structure and dynamics. We present preliminary results from the measurement of the chromatin compaction and nucleosome unwrapping dynamics at the single molecule level