1. Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, Department of Physics and Center for the Physics of Living Cells, Urbana, Illinois 61801, Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11 D-3707, Göttingen, Germany, Institute for Genomic Biology, University of Illinois, Champaign, Illinois 61801, and Howard Hughes Medical Institute, Urbana, Illinois 61801