MOE Key Laboratory of Bioinformatics, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China. zhangsong04@mails.tsinghua.edu.cn|MOE Key Laboratory of Bioinformatics, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China. zhangsong04@mails.tsinghua.edu.cn|MOE Key Laboratory of Bioinformatics, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China. zhangsong04@mails.tsinghua.edu.cn|MOE Key Laboratory of Bioinformatics, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China. zhangsong04@mails.tsinghua.edu.cn