1. Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, U.K.
2. Instituto de Investigaciones Citológicas, Amadeo de Saboya 4, 46010-Valencia, Spain
3. Department of Biochemistry, University of Utah Medical Center, 50 North Medical Drive, Salt Lake City, UT 84132, U.S.A.
4. August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen O, Denmark
5. The Tokyo Metropolitan Institute of Medical Science 18-22, Honkomagome 3-chome, Bunkyo-ku, Tokyo 113, Japan
6. MRC Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, DuCane Road, London W12 0NN, U.K.