Center for Bioinformatics, University of Tübingen, 72076 Tübingen, Germany, Applied Bioinformatics, Department of Computer Science, 72076 Tübingen, Germany, Quantitative Biology Center, 72076 Tübingen, Germany and Faculty of Medicine, University of Tübingen, 72076 Tübingen, Germany Center for Bioinformatics, University of Tübingen, 72076 Tübingen, Germany, Applied Bioinformatics, Department of Computer Science, 72076 Tübingen, Germany, Quantitative Biology Center, 72076 Tübingen, Germany and Faculty of Medicine, University of Tübingen, 72076 Tübingen, Germany.