1. Department of Biochemistry and Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, P.O. Box 594, Sheffield S10 2UH, United Kingdom, and Biotechnology Research Center, Toyama Prefectural University, 5180 Kurokawa, Kosugi, Toyama 939-03, Japan