1. Regulatory Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037.
2. Department of Biology, University of California, San Diego, CA 92093.
3. Institut für Molekularbiologie und Tumorforschung, Emil-Mannkopff-Strasse 1, D-3550 Marburg, FRG.
4. Metabolic Research Unit, Departments of Medicine and Biochemistry/Biophysics, University of California, San Francisco, CA 94143.