Department of Genome Regulation, Max Planck Institute for Molecular Genetics, Berlin, Germany.|Department of Genome Regulation, Max Planck Institute for Molecular Genetics, Berlin, Germany.|Department of Genome Regulation, Max Planck Institute for Molecular Genetics, Berlin, Germany.|Department of Genome Regulation, Max Planck Institute for Molecular Genetics, Berlin, Germany.|Department of Genome Regulation, Max Planck Institute for Molecular Genetics, Berlin, Germany.