1. Department of Biology, Pennsylvania State University, University Park, PA 16802, USA
2. Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA
3. Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802, USA
4. Department of Microbiology & Molecular Genetics, School of Medicine, University of California, Irvine, CA 92697, USA
5. Systems Biology Center, National Heart, Lung, and Blood Institute, NIH, Bethesda, Rockville, MD 20892, USA