Biophysics Graduate Group and Department of Molecular and Cellular Biology, University of California, Berkeley, California, United States of America. alistair@berkeley.edu|Biophysics Graduate Group and Department of Molecular and Cellular Biology, University of California, Berkeley, California, United States of America. alistair@berkeley.edu|Biophysics Graduate Group and Department of Molecular and Cellular Biology, University of California, Berkeley, California, United States of America. alistair@berkeley.edu