1. Institute for Physical and Theoretical Chemistry, Rheinische Friedrich-Wilhelms-University Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany
2. Max Delbrück Center for Molecular Medicine, Robert Rössle Strasse 10, D-13125 Berlin, Germany
3. Department of Biology, Technische Universität Darmstadt, 64289 Darmstadt, Germany