1. MRC Laboratory of Molecular Biology, Cambridge CB2 2QH, U.K.
2. MRC Protein Phosphorylation Unit, Department of Biochemistry, University of Dundee, Dundee DD1 4HN, Scotland, U.K.
3. Innogenetics, Industriepark Zwijnaarde 7, Box 4, B-9052 Gent, Belgium
4. Laboratory of Neuropathology, Born-Bunge Foundation, University of Antwerp, B-2610 Wilrijk, Belgium