1. Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401
2. Howard Hughes Medical Institute, Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, California 92037
3. Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
4. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92037
5. Department of Biological Sciences, University of North Texas, Denton, Texas 76203-5017