Abstract
Found in all eukaryotic cells, linker histones H1 are known to bind to and rearrange nucleosomal linker DNA. In vitro, the fundamental nature of H1∕DNA interactions has attracted wide interest among research communities-from biologists to physicists. Hence, H1∕DNA binding processes and structural and dynamical information about these self-assemblies are of broad importance. Targeting a quantitative understanding of H1 induced DNA compaction mechanisms, our strategy is based on using small-angle x-ray microdiffraction in combination with microfluidics. The usage of microfluidic hydrodynamic focusing devices facilitates a microscale control of these self-assembly processes, which cannot be achieved using conventional bulk setups. In addition, the method enables time-resolved access to structure formation in situ, in particular, to transient intermediate states. The observed time dependent structure evolution shows that the H1∕DNA interaction can be described as a two-step process: an initial unspecific binding of H1 to DNA is followed by a rearrangement of molecules within the formed assemblies. The second step is most likely induced by interactions between the DNA and the H1's charged side chains. This leads to an increase in lattice spacing within the DNA∕protein assembly and induces a decrease in the correlation length of the mesophases, probably due to a local bending of the DNA.