Molecular Biology Institute, Center for Genomics and Proteomics, Dept. of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095-1570, USA. leec@mbi.ucla.edu|Molecular Biology Institute, Center for Genomics and Proteomics, Dept. of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095-1570, USA. leec@mbi.ucla.edu