1. P. K. Cooper, Life Sciences Division, Building 934, Lawrence Berkeley National Laboratory, University of California, 1 Cyclotron Road, Berkeley, CA 94720, USA.
2. T. Nouspikel and S. G. Clarkson, Department of Genetics and Microbiology, University Medical Center (CMU), 1211 Geneva 4, Switzerland.
3. S. A. Leadon, Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7512, USA.