1. J. Balbach, V. Forge, W. S. Lau, N. A. J. van Nuland, C. M. Dobson, Oxford Centre for Molecular Sciences, New Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QT, UK.
2. K. Brew, Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, FL 33101, USA.