1. Novartis Institutes for BioMedical Research (S.R.C., S.E.D., E.C.R., X.L., T.L.M.), Cambridge, Massachusetts 02139;
2. The Genomics Institute of the Novartis Research Foundation (L.V., N.M., P.A.M., P.K., E.S.), San Diego, California 92121;
3. Department of Cell Biology (N.M., E.S.), The Scripps Research Institute, La Jolla, California 92037