1. Department of Biology, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, ETH Zurich, CH-8093 Zurich, Switzerland.
2. Department of Biology, Institute of Molecular Systems Biology, Auguste-Piccard-Hof 1, ETH Zurich, CH-8093 Zurich, Switzerland.
3. Faculty of Science, University of Zurich, CH-8057 Zurich, Switzerland.