1. Department of Biochemistry, University of Surrey, Guildford, Surrey GU2 SXH, U.K.
2. Imperial Cancer Research Fund, Laboratory of Molecular Pharmacology and Drug Metabolism, Department of Biochemistry, Hugh Robson Building, George Square, Edinburgh EH8 9XD, U.K.
3. Department of Biological and Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, Northern Ireland, U.K.