Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA and Department of Human Biology, J. Craig Venter Institute, 4120 Capricorn Lane, La Jolla, CA 92037, USA.