1. European Molecular Biology Laboratory, Hamburg Outstation, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Federal Republic of Germany, Organic Macromolecular Chemistry, Postfach 151150, Saarland University, D-66041 Saarbrücken, Federal Republic of Germany, Synchrotron Radiation Research Section, MCL, NCI, Argonne National Laboratory, Argonne, Illinois 60439, York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, U.K., and Department of Biochemistry,...