1. Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, California Institute for Quantitative Biosciences, Center for RNA Systems Biology, University of California, San Francisco, San Francisco, CA 94158, USA.
2. Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA.
3. Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA 94158, USA.
4. Department of Biological Sciences, Stanford University, Stanford, CA 94025, USA.
5. Department of Applied Physics; Stanford University, Stanford, CA 94025, USA.
6. Department of Genetics, Stanford University, Stanford, CA 94025, USA.
7. Department of Bacteriology, University of Wisconsin, Madison, WI 53706, USA.