Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, United States of America.|Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, United States of America.|Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America.|Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California, United States of America.|Control and Dynamical Systems Option, Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, United States of America.|Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, United States of America.