1. Lawrence Berkeley National Laboratory, Berkeley, California 94720, Physics and Advanced Technology, Lawrence Livermore National Laboratory, Livermore, California 94551, Affymetrix Inc., 3420 Central Expressway, Santa Clara, California 95051, Department of Laboratory Medicine and the Comprehensive Cancer Center, University of California, San Francisco, California 94143, and Department of Chemistry, University of California at Berkeley, Berkeley, California 94143