Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, D-14195 Berlin, Germany and Department of Biosystems Science and Engineering, ETH Zurich and Swiss Institute of Bioinformatics, CH-4058 Basel, Switzerland.|Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, D-14195 Berlin, Germany and Department of Biosystems Science and Engineering, ETH Zurich and Swiss Institute of Bioinformatics, CH-4058 Basel, Switzerland Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, D-14195 Berlin, Germany and Department of Biosystems Science and Engineering, ETH Zurich and Swiss Institute of Bioinformatics, CH-4058 Basel, Switzerland.|Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, D-14195 Berlin, Germany and Department of Biosystems Science and Engineering, ETH Zurich and Swiss Institute of Bioinformatics, CH-4058 Basel, Switzerland.