1. S. Coats and J. M. Roberts, Department of Basic Sciences, Fred Hutchinson Cancer Research Center, 1124 Columbia Street, Seattle, WA 98104, USA.
2. W. M. Flanagan, Gilead Sciences, 346 Lakeside Drive, Foster City, CA 94404, USA.
3. J. Nourse, Program in Cancer Biology, Stanford University Medical School, Stanford, CA 94305, USA.