1. Institut de Biologia Molecular de Barcelona-CSIC, Parc Científic de Barcelona, Barcelona 08028, Spain
2. Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA 90095-1569, USA
3. Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem 91120, Israel
4. Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain