1. Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY;
2. Department of Medicine and Rosalind Russell Arthritis Center, University of California, San Francisco, San Francisco, CA;
3. Medical Service, Veterans Administration Medical Center, San Francisco, CA;
4. Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Weill Hall, Ithaca, NY; and
5. Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge, United Kingdom