1. K. C. Garcia, M. Degano, R. L. Stanfield, and I. A. Wilson are at the Department of Molecular Biology and the Skaggs Institute of Chemical Biology, Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
2. A. Brunmark, M. R. Jackson, P. A. Peterson, and L. Teyton are at the R. W. Johnson Pharmaceutical Research Institute-La Jolla, 3535 General Atomic Court, San Diego, CA 92121, USA.