1. Centre for Biomolecular Science, The University, St. Andrews KY16 9ST, U.K.
2. Institut de Biochemie et de Génétique Cellulaires du CNRS, Université Victor Segalen, Bordeaux 2, 1 rue Camille Saint-Saëns, F-33 077 Bordeaux cedex, France
3. Max-Planck-Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
4. Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53705, U.S.A.
5. Department of Microbiology, University of Guelph, Guelph, Canada N1G 2W1