1. Institute of Biochemistry, University of Lübeck, D-23538 Lübeck, Germany.
2. Institute of Molecular Biotechnology, D-07745 Jena, Germany.
3. Institute of Virology and Immunology, University of Würzburg, D-97078 Würzburg, Germany.
4. Institute of Molecular Biology, University of Jena, D-07745 Jena, Germany.