About the Authors
Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: ELJ GWD. Performed the experiments: ELJ RDF. Analyzed the data: ELJ RDF. Contributed reagents/materials/analysis tools: ELJ. Wrote the paper: ELJ GWD.