1. MRC Protein Phosphorylation and Ubiquitylation Unit, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, U.K.
2. Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02115, U.S.A.
3. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, SGM 628, Boston, MA 02115, U.S.A.
4. Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, U.K.