1. MOE Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing 100084, China
2. Center for Epigenetics, Van Andel Institute, Grand Rapids, MI 49503, USA
3. Tsinghua-Peking Center for Life Sciences, Beijing 100084, China