1. National Laboratory of Genomics, Cinvestav, Carretera Irapuato-Leon Km 9.6, Irapuato, Guanajuato 033600, México
2. Laboratorio de Investigación Bioquímica, Programa Institucional en Biomedicina Molecular ENMyH-Instituto Politécnico Nacional, Guillermo Massieu Helguera No. 239, La Escalera Ticoman 07320, D.F, México
3. Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Ave., Box 8231, St. Louis, MO 63110, U.S.A.