1 Gene Center and Department of Biochemistry, University of Munich, Feodor-Lynenstr. 25, 81377 Munich, Germany. Electronic address: Wilson@lmb.uni-muenchen.de.
2 Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany. Electronic address: christian.spahn@charite.de.
3 Institute of Genetics and Molecular and Cellular Biology, 1 rue Laurent Fries, 67404 Illkirch, CEDEX, France. Electronic address: marat@igbmc.fr.