1. Howard Hughes Medical Institute (W.X., R.M.E.), California 92037
2. Gene Expression Laboratory (W.X., N.N.Y., R.J.L., C.M.S., R.M.E.) The Salk Institute for Biological Studies La Jolla, California 92037
3. Department of Pathology (H.H., M.R.S.) University of Southern California Los Angeles, California 90033