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BP: Fachverband Biologische Physik

BP 7: Poster I

BP 7.53: Poster

Monday, March 23, 2009, 17:45–20:00, P3

TmHU-DNA binding studied by atomic force microscopy — •Hergen Brutzer, Mathias Salomo, Friedrich Kremer, and Ulrich Keyser — Institute for Experimental Physics I, Leipzig University, Linnéstraße 5, D-04103 Leipzig, Germany

In contrast to the well-characterized processes of formation and destabilization of complexes from eukaryotic histones with DNA, little is known about interactions between histone-like proteins from prokaryotes and DNA. These proteins also kink and bend DNA leading to chromatin-like structures. The histone-like HU protein is nearly ubiquitous in all bacteria. Especially TmHU from Thermotoga maritima exhibits some extraordinary properties, such as the protection of DNA inside the bacterium against thermal denaturation. Experiments with optical tweezers suggest the existence of a threshold protein concentration for the formation of TmHU-DNA complexes. Here we use atomic force microscopy to study the concentration dependence by alternative means and minimize influence by external forces. The end-to-end distance and the height of the complexes were measured in dependence of protein concentration (50-5000 nM). With increasing protein concentration the end-to-end distance decreases from 70 to 38 nm while the height increases from 0.7 to 2.2 nm for 250 bp dsDNA, indicative of the formation of a globular structure of the TmHU-DNA complex. Most likely this originates from a secondary organizational level during TmHU-DNA binding observed in optical tweezers experiments.