1. Investigators in the Department of Biological Chemistry at Harvard Medical School, Boston, Massachusetts 02115.
2. MRC Senior Fellow in the Department of Genetics, Cambridge University, Cambridge CB2 3EH, England.
3. Graduate student in the Department of Biochemistry at Stanford University School of Medicine, Stanford, California 94305.
4. Investigator in the Department of Molecular Biology, University of Geneva, 1211 Geneva 4, Switzerland.
5. Professor in the Division of Biology, California Institute of Technology, Pasadena 91125.
6. Professor in the Department of Biochemistry at Stanford University School of Medicine, Stanford, California 94305.