Since the discovery of the right-handed helical structure of DNA, 61 years have passed. The DNA molecule, which encodes genetic information, is also found twisted into coils. This extra twist of... Show moreSince the discovery of the right-handed helical structure of DNA, 61 years have passed. The DNA molecule, which encodes genetic information, is also found twisted into coils. This extra twist of the helical structure, called supercoiling, plays important roles in both DNA compaction and gene regulation. The DNA in eukaryotic cells is packaged into chromatin. Using single-molecule force spectroscopy, I resolved force/torque induced structural changes of DNA and chromatin fibers. I showed that the structural changes of chromatin fibers can be described by four conformations. I showed for the first time the folding and unfolding of a chromatin fiber under torsion. Th e anisotropic response of chromatin fibers to supercoiling reflects its leftŸ-handed chirality. These findings give a detailed structural insight of a supercoiled chromatin fiber, yielding a better understanding of the response of chromatin during transcription Show less
Understanding of chromatin organization and compaction in Archaea is currently limited. The genome of several megabasepairs long is folded by a set of small chromatin proteins to fit into the... Show moreUnderstanding of chromatin organization and compaction in Archaea is currently limited. The genome of several megabasepairs long is folded by a set of small chromatin proteins to fit into the micron-sized cell. A first step in understanding archaeal chromatin organization is to study the action of individual chromatin proteins on DNA. Characterization of the architectural properties of these proteins is essential to understand how they shape and modulate the archaeal genome. This thesis describes the biophysical characterization of several chromatin proteins from the crenarchaeal model organism Sulfolobus solfataricus: Cren7, Sul7, Alba and Sso10a. The architectural properties of these proteins resemble those of their bacterial counterparts, suggesting that they could play a similar role in chromatin organization and global gene regulation. Show less
