1. Department of Cancer Biology, Glaxo Wellcome Research and Development, Research Triangle Park, NC 27709
2. Department of Protein Sciences, Glaxo Wellcome Research and Development, Research Triangle Park, NC 27709; Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6059
3. Department of Protein Sciences, Glaxo Wellcome Research and Development, Research Triangle Park, NC 27709