Ionizing radiation and DNA double-strand breaks (DSB) induced by radiation are part of the everyday stresses of an organism. Every cell has different repair mechanisms to counteract this health threat. However, ionizing radiation also offers potentially important medical applications such as radiation therapy for the treatment of tumours. Researching the underlying DNA repair processes not only makes it possible to provide better protection against ionizing radiation in the future, but also to make the targeted use of radiation in medical settings even more efficient. Not only the identification of individual DNA repair proteins and the quantification of the induced damage is important, but also the localization of the damage in the context of chromatin helps to better understand the repair processes and to optimize medical approaches. This work focuses on three main aspects for the characterization of DSB repair mechanisms. A new method for the quantitative measurement of high-LET (Linear Energy Transfer) induced radiation damage was developed and the corresponding proof of principle was provided. Using in situ ligation techniques in combination with in situ DNA blunting, it was possible to couple so-called DNA oligo probes, consisting of short single-stranded DNA sequences that form hairpin structures in solution, with fluorophores and specifically bind them to double-strand breaks. The reduced size and the reduced number of binding sites allows an accurate and reliable DSB detection using STED microscopy (Stimulated Emission Depletion). In addition, irradiation experiments with focused carbon ions made it possible not only to trigger the most basic reactions of chromatin to irradiation with high-LET radiation and to document them by live cell microscopy, but also to observe these chromatin remodeling processes from a few seconds to several minutes after irradiation and to compare them with characteristics of several repair proteins. It was also possible to establish a detailed model for DNA repair in the context of chromatin organisation and in accordance with the latest chromatin organisation models by the high-resolution analysis of overlapping regions of the DNA repair proteins BRCA1, Rad51, 53BP1, γH2AX and components of the chromatin. In addition, in the course of this work, ∝ - irradiation of cell nuclei - was used for the first time to document a migration of difficult to repair DSB repair sites from the cell nucleus interior to the cell nucleus envelope and presumably to specialized repair centers. Also, it was possible to match them temporally into existing DSB repair processes using STED microscopy.    «

Ionizing radiation and DNA double-strand breaks (DSB) induced by radiation are part of the everyday stresses of an organism. Every cell has different repair mechanisms to counteract this health threat. However, ionizing radiation also offers potentially important medical applications such as radiation therapy for the treatment of tumours. Researching the underlying DNA repair processes not only makes it possible to provide better protection against ionizing radiation in the future, but also to m...    »