1. M. Ormö, K. Kallio, S. J. Remington, Institute of Molecular Biology and Department of Physics, University of Oregon, Eugene, OR 97403-1226, USA.
2. A. B. Cubitt, Aurora Biosciences, 11149 North Torrey Pines Road, La Jolla, CA 92037, USA.
3. L. A. Gross and R. Y. Tsien, Department of Pharmacology and Howard Hughes Medical Institute 0647, University of California, San Diego, La Jolla, CA 92093-0647, USA.