1. D. A. Fruman. C. M. Yballe, J. Y. Yu, L. C. Cantley, Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02215, and Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. S. B. Snapper, Department of Medicine, Harvard Medical School, Boston, MA 02115; Howard Hughes Medical Institute, Children's Hospital, Boston, MA 02115; Center for Blood Research, Boston, MA 02115; and Gastrointestinal Unit (Medical Services), Massachusetts General Hospital, Boston,...