Department of Biology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology (ETH Zurich), CH-8093 Zurich, Switzerland. abdullah@imsb.biol.ethz.ch|Department of Biology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology (ETH Zurich), CH-8093 Zurich, Switzerland. abdullah@imsb.biol.ethz.ch|Department of Biology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology (ETH Zurich), CH-8093 Zurich, Switzerland. abdullah@imsb.biol.ethz.ch