About the Authors
Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States of America
The authors have declared that no competing interests exist.
ND, MP, PVK, NB, and RVR performed the experiments and analyzed the data. HS conceived and designed the experiments, analyzed the data, and wrote the paper.