1. Research Center CAESAR, Ludwig-Erhard-Allee 2, D-53175 Bonn, Germany, Institute of Virology of the University Cologne, Fürst Pückler Strasse 56, D-50935 Cologne, Germany, Menterstrasse 141, D-81247 München, Germany, QIAGEN GmbH, Qiagen Str. 1, D-40724 Hilden, Germany, Faculty of Engineering, University of Kiel, Kaiserstrasse 2, D-24143 Kiel, Germany, and LIMES Institute, Program Unit Chemical Biology & Medicinal Chemistry, University of Bonn, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany