M. XIANG, 1 L. GAN, 2 D. LI, 3 L. ZHOU, 4'6 Z.-Y. CHEN, 1 D. WAGNER, 2 B .W. O'MALLEY, JR., 3 W. KLEIN, 2 J . NATHANS 4'5'6 1Center for Advanced Biotechnology and Medicine, Department of Pediatrics, UMDNJ-Robert Wood Johnson 2 Medical School, Piscataway, New Jersey 08854; Department of Biochemistry and Molecular Biology, University 3 of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Departments of Otolaryngology, Head and Neck Surgery, 4Molecular Biology and Genetics, 5Neuroscience, and ~Ophthalmology, 6Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205