1. WSL Swiss Federal Research Institute; Zürcherstrasse 111 8903 Birmensdorf Switzerland
2. Department of Biology; Virginia Commonwealth University; Richmond VA 23284 USA
3. Faculty of Molecular Biology; Max F. Perutz Laboratories and University of Vienna; Oskar-Morgenstern-Platz 1 1090 Vienna Austria
4. ETH Zürich; Institute of Integrative Biology; Universitätstrasse 16 8092 Zürich Switzerland