1. Life Sciences and Technology; Beuth University of Applied Sciences Berlin; D-13347 Berlin Germany
2. Department of Microbiology and Molecular Genetics; The University of Texas Medical School at Houston, 6431 Fannin St; Houston TX 77030 USA
3. Institute of Structural and Molecular Biology, University College London and Birkbeck College; London WC1E 7HX UK
4. Division of Microbiology, Department of Biology; Friedrich Alexander University Erlangen-Nuremberg; D-91058 Erlangen Germany