1. Department of Medicinal Chemistry, Box 357610, University of Washington, Seattle, Washington 98195
2. Department of Biological Structure, Biomolecular Structure Center, Box 357420, University of Washington, Seattle, Washington 98195
3. Department of Cell and Molecular Biology, Uppsala University, Biomedical Center, Box 596, SE-751 24 Uppsala, Sweden
4. Department of Biochemistry and Organic Chemistry, Uppsala University, Biomedical Center, Box 576, SE-751 23 Uppsala, Sweden