Compaction of Single-Molecule Megabase-Long Chromatin under the Influence of Macromolecular Crowding

The megabase-sized length of chromatin is highly relevant to the state of chromatin in vivo, where it is subject to a highly crowded environment and is organized in topologically associating domains of similar dimension. We developed an in vitro experimental chromatin model system reconstituted from T4 DNA (approximately 166 kbp) and histone octamers and studied the monomolecular compaction of this megabase-sized chromatin fiber under the influence of macromolecular crowding. We used single-molecule fluorescence microscopy and observed compaction in aqueous solutions containing poly(ethylene glycol) in the presence of monovalent (Na+ and K+) and divalent (Mg2+) cations.

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