1. The Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, Department of Chemistry & Biochemistry, 0303, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0303, and Division of Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, CH-3012 Berne, Switzerland