1. Physics Department and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
2. Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
3. Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
4. Howard Hughes Medical Institute, University of Illinois, Urbana, IL 61801, USA.