1. Center for Mechanistic Biology and Biotechnology, Argonne National Laboratory, Argonne, Illinois 60439, M. A. Cunningham Associates, Northbrook, Illinois 60062, J. W. Gibbs Laboratory, Department of Physics, Yale University, New Haven, Connecticut 06511, InPharmatics Corporation, San Diego, California 92126, and Cornell Theory Center, Cornell University, Ithaca, New York 14853