About the Authors
Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California, United States of America
Howard Hughes Medical Institute, University of California, San Francisco, California, United States of America
The authors have declared that no conflicts of interest exist.
SS and PW conceived and designed the experiments. SS performed the experiments. SS analyzed the data. SS contributed reagents/materials/analysis tools. SS, RMS, and PW wrote the paper.