Departments of Vertebrate Genomics and Developmental Biology, Max Planck Institute for Molecular Genetics, Ihnestrasse 63-73, 14195 Berlin, Germany, Department of Rheumatology and Clinical Immunology, Institute of Pathology, Laboratory of Molecular Tumour Pathology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany and Division of Signaling and Gene Expression, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA.