Center for Bioinformatics, University of Tübingen, Tübingen, Germany.|Center for Bioinformatics, University of Tübingen, Tübingen, Germany.|Center for Bioinformatics, University of Tübingen, Tübingen, Germany.|Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America.|Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America.|Center for Bioinformatics, University of Tübingen, Tübingen, Germany.