1. Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria.
2. Department of Biology, Institute of Molecular Systems Biology, Eidgenössische Technische Hochschule (ETH) Zürich, 8093 Zurich, Switzerland.
3. Department of Biochemistry, Gene Center, Ludwig-Maximilian University, 81377 Munich, Germany.