1. J. A. Le Good, W. H. Ziegler, D. B. Parekh, P. J. Parker, Protein Phosphorylation Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK. D. R. Alessi, and P. Cohen, Department of Biochemistry, Medical Sciences Institute, Dundee University, Dundee DD1 4HN, UK.