About the Authors
Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: AML MG. Performed the experiments: AML. Analyzed the data: AML MG. Contributed reagents/materials/analysis tools: AML MG. Wrote the paper: AML MG.