Institution: | From the ‡Department of Biology, Stanford University, Stanford, California 94305.;the §Department of Pharmacology, University of Colorado Denver School of Medicine, Aurora, Colorado 80045.;the ¶Laboratory of Cell Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892, and ;the ‖Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 |