1. Department of Cell Biology, Vanderbilt University School of Medicine (L.H.H., G.E.O.), Nashville, Tennessee 37232
2. Department of Biochemistry and Molecular Biology, M. D. Anderson Cancer Center (D.D.C.), Houston, Texas 77030
3. Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center (B.S.C.), Lubbock, Texas 79430