1. Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow Gl 2 8QQ, Scotland, U.K.
2. Hans-Knöll-lnstitut für Naturstoff-Forschung, Beutenbergstrasse 11, D-087745 Jena, Federal Republic of Germany
3. Friedrich Miescher-lnstitut, P.O.B. 2543, CH-4002 Basel, Switzerland
4. Dipartimento di Biopatologia Umana, Universita degli Studi di Roma ‘La Sapienza’, Via Regina Elena 324, 00161 Roma, Italy