1. Department of Biochemistry, Michigan State University, East Lansing, MI 48824
2. Current address: Plant Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, A.C.T. 2601, Australia
3. Current address: Public Affairs Department, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724
4. Institute of Biological Chemistry, Washington State University, Pullman, WA 99164