1. Institute for Virology and Immunobiology, D-97078 Würzburg, Germany.
2. Institute of Human Genetics, University of Würzburg, Biozentrum, D-97074 Würzburg, Germany.
3. CNRS UPR420, Genetique Moleculaire et Biologie du Development 7, F-94801 Villejuif Cedex, France.