Auger electron emitter labeled oligonucleotides and base analogs are used to induce DNA damage in selected cell lines. Specific labeling techniques and the selection of oligonucleotides can be used to induce both single and multiple DNA damages at defined locations in the genome. Using high-resolution microscopy techniques (fluorescence localization microscopy (Heidelberg subproject) and transmission electron microscopy (Homburg subproject)), the topological changes in the chromatin environment after damage and during the subsequent repair processes are systematically investigated in the immediate and distant vicinity of the damage site. For this purpose, hetero- and euchromatin are specifically labeled and analyzed using antibodies as well as repetitive sequences using fluorescent oligonucleotides. Topologies of strand breaks (break ends), target regions (γH2AX foci) and repair foci (recruitment of relevant DNA repair proteins) will be detected by high-resolution microscopy techniques and analyzed by mathematical methods. By systematic comparison, characteristic parameters of chromatin and repair foci architecture will be determined and the importance for repair progression and intrinsic radioresistance of the selected cells will be correlated.