1 Department of Biology of the Cell Nucleus, Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic, v.v.i., 142 20 Prague, Czech Republic.
2 Department of Biology of the Cell Nucleus, Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic, v.v.i., 142 20 Prague, Czech Republic; Department of Epigenetics of the Cell Nucleus, Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic, v.v.i., division BIOCEV, 25250 Vestec, Czech Republic; Microscopy Centre, Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic, v.v.i., 142 20 Prague, Czech Republic. Electronic address: hozak@img.cas.cz.