1. Department of Cell and Molecular Biology (E.T.M., C.A.P., J.C., M.H.-D.) Northwestern University Medical School Chicago, Illinois 60611
2. Department of Biochemistry, Molecular Biology and Cell Biology (A.M., K.E.M.) Northwestern University Evanston, Illinois 60208
3. Intramural Research Support Program (G.S.) SAIC-Frederick National Cancer Institute Frederick Cancer Research and Development Center Frederick, Maryland 21702-1201