Max Planck Institute for Molecular Genetics, Department of Computational Molecular Biology, Ihnestrasse 63-73, D-14195 Berlin, Germany. stefanie.scheid@molgen.mpg.de|Max Planck Institute for Molecular Genetics, Department of Computational Molecular Biology, Ihnestrasse 63-73, D-14195 Berlin, Germany. stefanie.scheid@molgen.mpg.de