1. Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720–3220, USA.
2. California Institute for Quantitative Biosciences, University of California Berkeley, Berkeley, CA 94720–3220, USA.
3. Biophysics Graduate Program, University of California Berkeley, Berkeley, CA 94720–3220, USA.
4. Department of Chemistry, Pennsylvania State University, University Park, PA 16802, USA.