1. Department of Biochemistry, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294.
2. Department of Pediatrics and Department of Biochemistry and Biophysics, The Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA 19104.
3. Department of Biochemistry, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195.
4. Laboratory of Reproductive Physiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.