1. Pennsylvania State University, University Park, Pennsylvania 16804-3000, Jmol Project, U. S. A., Cornell University, Ithaca, New York 14853, Cambridge University, Cambridge CB2 1TN, Great Britain, Imperial College, London SW7 2AZ, Great Britain, Cologne University Bioinformatics Center (CUBIC), Zülpicher Str. 47, D-50674 Köln, Germany, University of Tübingen, Tübingen, Germany, and Jmol project, The Netherlands