1. Centre for Molecular Cell Biology, Department of Medicine, Royal Free and University College Medical School, University College London, Rowland Hill Street, London, NW3 2PF, UK
2. Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale, 66030 Santa Maria Imbaro (Chieti), Italy
3. Department of Biochemistry, University of Bristol, School of Medical Sciences, University Walk, Bristol, BS8 1TD, UK
4. CRUK Institute for Cancer Studies, University of Birmingham, Edgbaston, Birmingham, B15 2TA, UK