John van Noort Lab - Chromatin DynamicsC FvL1

Chromatin is an ubiquitous protein-DNA complex that forms the structural basis of DNA condensation in all eukaryotic organisms. Packaging and depackaging of such chromatin, called chromatin remodelling, plays a central role in all cellular processes that involve chromosomes such as transcription, replication, recombination, repair etc. Detailed knowledge of the principles and mechanisms underlying this control of DNA condensation is thus vital for understanding many diseases, including cancer.
Eukaryotic cells have two major pathways to control DNA condensation. First, a large and very diverse group of enzymes has been found to chemically modify histone tails. Some of these covalent modifications, like acetylation, have been shown to modulate packaging of DNA. Alternatively, histone modifications may act as a docking site for additional chromatin processing enzymes. Second, ATP-dependent remodellers have been identified and are thought to move over DNA, and while doing so release DNA from histones.


The physical mechanisms governing these processes however, are still largely unknown. In our group we develop and use modern biophysical techniques to unravel the physics behind DNA condensation. Since many of the processes that modulate DNA condensation depend on inter- and intra- molecular forces, single-molecule force spectroscopy is the technique of choice for such studies. For obtaining structural data on the dynamics of biomolecules at the scale of 1-10 nm, i.e. the size of a histone and also the range of most relevant physical interactions, single pair Fluorescence Resonance Energy Transfer has proven invaluable. At a larger scale, Atomic Force Microscopy provides a unique tool for imaging and manipulation of chromatin fibers in vitro. All these single-molecule techniques have in common that no time and ensemble averaging occurs, which makes them particularly useful to address these complex biochemical reactions in which multiple components act independently. We are currently developing state-of-the-art single-molecule manipulation techniques, i.e. optical and magnetic tweezers, sp-FRET microscopy and video AFM, to allow for a rigorous biophysical characterization of the dynamics of these processes.