1. M. I. Aladjem, L. L. Brody, G. M. Wahl, Gene Expression Laboratory, Salk Institute, 10010 North Torrey Pines Road, San Diego, CA 92037, USA.
2. M. Groudine and E. M. Epner, Fred Hutchinson Cancer Research Center, Seattle, WA 98185, USA, and University of Washington, Seattle, WA 98195, USA.
3. E. S. Dieken and R. E. Keith Fournier, Fred Hutchinson Cancer Research Center, Seattle, WA 98185, USA.