1. Epithelial Biology Unit, The Ronald O. Perelman Department of Dermatology, New York, New York 10016
2. Department of Pharmacology, New York, New York 10016
3. Skirball Institute of Biomolecular Medicine, New York, New York 10016
4. Department of Urology, New York, New York 10016
5. Department of Microbiology, Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, New York 10016
6. Veterans Administration Medical Center, New York, New York 10010
7. Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892