1. S. L. Coon, P. H. Roseboom, R. Baler, J. L. Weller, D. C. Klein, Section on Neuroendocrinology, Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
2. M. A. A. Namboodiri, Department of Biology, Georgetown University, Washington, D. C. 20057, USA.
3. E. V. Koonin, National Center for Biotechnology Information, National Library of Medicine, Bethesda, MD 20894, USA.