1. Department of Physiology and Biophysics, Mount Sinai School of Medicine, One Gustave L. Levy Place, P.O. Box 1218, New York, New York 10029, and Bioinformatics Unit, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain