1. Institute of Biochemistry, Pfaffenwaldring 55, Faculty of Chemistry, University of Stuttgart, D-70569 Stuttgart, Germany
2. Epigenetics Programme, The Babraham Institute, Cambridge CB22 3AT, UK; The Welcome Trust Sanger Institute, Cambridge CB10 1SA, UK
3. The Babraham Institute, Cambridge CB22 3AT, UK
4. Max Planck Genome-Centre Cologne, Carl-von-Linné-Weg 10, D-50829 Cologne, Germany