About the Authors
Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: SJK ZJH. Performed the experiments: SJK JL MSL ZJH. Analyzed the data: SJK MSL ZJH. Contributed reagents/materials/analysis tools: SJK ZJH. Wrote the paper: SJK ZJH.