1. Centro de Ciencias Genómicas; Universidad Nacional Autónoma de México; Av. Universidad s/n, Apdo. Postal 565-A Cuernavaca Morelos CP62210 Mexico
2. Department of Biologic and Materials Sciences; University of Michigan School of Dentistry; Ann Arbor Michigan 48109 USA
3. Department of Biochemistry; Duke University Medical Center; Durham North Carolina 27710 USA