1. Department for Molecular Biomedical Research, VIB, B-9052 Ghent, Belgium
2. Department of Biomedical Molecular Biology, Ghent University, B-9052 Ghent, Belgium
3. Max Planck Institute of Biochemistry, D-82152 Martinsried, Germany
4. Institute for Genetics, University of Cologne, D-50674 Cologne, Germany