Otto-Warburg Laboratory, Max Planck Institute for Molecular Genetics (MPIMG), Berlin, Germany. woodsmit@molgen.mpg.de|Otto-Warburg Laboratory, Max Planck Institute for Molecular Genetics (MPIMG), Berlin, Germany. woodsmit@molgen.mpg.de|Otto-Warburg Laboratory, Max Planck Institute for Molecular Genetics (MPIMG), Berlin, Germany. woodsmit@molgen.mpg.de