1. Division of Yeast Genetics, National Institute for Medical Research, The Ridgeway, London NW7 1AA, United Kingdom;
2. Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130;
3. Department of Molecular Microbiology, Research Institute for Microbial Diseases, Osaka University, Osaka 565, Japan; and
4. Department of Biochemistry and Genetics, Medical School, University of Newcastle, Newcastle-Upon-Tyne NE2 4HH, United Kingdom