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Nucleosome stacking in chromatin fibers probed with single-molecule force- and torque-spectroscopy

woensdag 19 juni 2019
Rapenburg 73
2311 GJ Leiden


In human cells, a meter-long DNA is condensed inside a micrometer-sized cell nucleus. Simultaneously, the genetic code must remain accessible for its replication and transcription to functional proteins. Such plasticity of the genome is maintained by dynamic folding and unfolding of DNA-protein spools called nucleosomes. It is unclear, however, how this process is controlled when multiple nucleosomes stack on top of each other and form compact chromatin fibers. This is particularly important since nucleosomes are rarely present in isolation inside a densely packed cell nucleus. Yet, most of the mechanistic studies on chromatin have focused so far only on individual nucleosomes or sparsely decorated nucleosomal arrays. Therefore, the aim of this thesis was to increase the understanding of the chromatin fiber structure and its dynamics. Knowing these details would provide many new insights into the mechanisms of gene expression (epigenetic regulation) which, upon malfunction, may cause severe diseases. The presented work consists of an experimental approach involving the application of single-molecule force spectroscopy, and makes use of theoretical modelling based on statistical mechanics. By using magnetic tweezers, we stretched and twisted individual chromatin fibers reconstituted in vitro in order to unfold its nucleosomes. We investigated how the spacing between nucleosomes, supercoiling, and the "linker histone" protein affect the stability and elasticity of chromatin. These studies show that folding of nucleosomes into chromatin fibers opens up a plethora of regulatory pathways for controlling the level of DNA organization in cells.


  • Prof.dr.ir. S.J.T. van Noort
  • Prof.dr. N.H. Dekker (Delft)


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