1. Rega Institute for Medical Research, K. U. Leuven, B-3000 Leuven, Belgium
2. Karolinska Institute, Huddinge University Hospital, S-141 86 Huddinge/Stockholm
3. Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, Oxford OX3 7BN, United Kingdom
4. Medivir AB, S-141 11 Huddinge, Sweden