1. Schools of *Biosciences and
2. Centre de Recherches de Biochimie Macromoléculaire, Centre National de la Recherche Scientifique FRE2593, 34293 Montpellier, Cedex 5, France
3. Medicine, The University of Birmingham, Birmingham, Edgbaston, West Midlands, B15 2TT, United Kingdom; and