1. Institute of Microbiology, Academy of Sciences of the Czech Republic, 142 20 Prague 4-Krč, Czech Republic, Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6-Dejvice, Czech Republic, and Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 142 20 Prague 4-Krč, Czech Republic