1. D. Pruss and A. P. Wolffe, Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, National Institutes of Health, Building 6, Room B1A-13, Bethesda, MD 20892-2710, USA.
2. B. Bartholomew and J. Persinger, Department of Medical Biochemistry, Southern Illinois University at Carbondale, School of Medicine, Carbondale, IL 62901-4413, USA.
3. J. Hayes, Department of Biochemistry, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, USA.
4. G. Arents and E. N. Moudrianakis, Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.